Muggles' Guide to Harry Potter/Characters/Severus Snape

Overview
 Severus Snape is the Potions teacher at Hogwarts School of Witchcraft and Wizardry. He is also the Head of Slytherin House and briefly served as Headmaster in book 7. Although Snape is a former Death Eater, Professor Dumbledore places his utmost faith in Snape's loyalty, though exactly why he trusts him so implicitly is initially unknown. Snape joins the Order of the Phoenix to combat Lord Voldemort, apparently acting as a double agent, though, later, Snape also serves Lord Voldemort. Snape's true loyalties remain uncertain until the final book.

According to the author, Severus Snape's birthday is 9 January 1960 and he died on 2 May 1998 at the age of 38. It is unknown what wood and core comprise Snape's wand.

Philosopher's Stone
Harry Potter's first interaction with Professor Snape is minor, but telling; as Snape glares at him across the Great Hall, Harry's forehead scar starts throbbing. The scar is a link between Harry and Lord Voldemort, the evil wizard who inflicted it, and this may be a connection between Snape and Voldemort. Other possibilities are discussed later. That night, Harry dreams about Professor Quirrell's turban, and Draco Malfoy turning into Snape.

During Potions class, Snape humiliates Harry by asking questions he could not know the answers to, though implying that he should. When Neville melts his cauldron during class, Snape blames Harry, and penalises Gryffindor house a point.

During the Hallowe'en feast, a giant troll enters the dungeons, though rather than follow the other teachers there, Snape instead rushes upstairs, possibly to the corridor Professor Dumbledore declared off-limits. Hermione, Ron, and Harry later notice Snape limping, and Harry sees Filch tending Snape's wound and overhears Snape mention something with three heads. The Trio speculate Snape was wounded by the giant three-headed dog that is guarding a trap door in the forbidden corridor.

At the Quidditch match against Slytherin, Snape appears to be jinxing Harry's broom until Hermione distracts Snape by setting his robes on fire. Hagrid later defends Snape, and surprisingly admits to the Trio that the three-headed dog is his pet and is actually quite tame.

Snape fills in as the Quidditch referee for Madam Hooch; Harry, believing Snape is using this as a cover for another attempt on his life, catches the Snitch almost immediately, ending the game.

After Harry overhears Snape arguing with Professor Quirrell about his loyalties, Harry, Hermione, and Ron conclude that Snape is after the Philosopher's Stone for Voldemort, and only Quirrell stands between it and the Dark Lord. Hagrid's claiming that Snape is helping protect the Stone only causes the Trio more concern. Harry believes that once Voldemort is resurrected, he will kill Harry. The Trio venture through the trap door under Fluffy, to retrieve the Stone before Snape can.

In the climactic scene between Professor Quirrell and Harry, Quirrell reveals that he (Quirrell) seeks the Stone for Voldemort; Snape was actually thwarting Quirrell's efforts to jinx Harry's broom during the Quidditch game. Harry's scar had hurt during Arrival Feast because of Quirrell's connection to Voldemort; Snape was then talking to Quirrell, allowing Voldemort, from the back of Quirrell's head, to sense Harry's presence.

Chamber of Secrets
After Harry and Ron crash the flying car into the Whomping Willow, Snape arrives and takes them to his office. The  Evening Prophet reports that Muggles sighted a flying car. When Professor McGonagall and Professor Dumbledore arrive, Snape wants Harry and Ron expelled from Hogwarts. After sternly warning them, Dumbledore says it is up to McGonagall to determine the boys' punishment.

Snape allows the Slytherin team to unfairly usurp the Quidditch pitch during Gryffindor's practice time, "so that they may train their new Seeker", Draco Malfoy. It seems that Mr. Malfoy has donated expensive new broomsticks to the Slytherin team.

When Filch's cat, Mrs. Norris, is found petrified, Snape questions why Harry, Ron, and Hermione were absent from the Hallowe'en Feast, and seems skeptical when they claim they instead attended Nearly Headless Nick's Deathday party. Snape suspects Harry may be involved with Mrs. Norris being petrified, and recommends banning him from Quidditch until he is ready to be honest. Professor McGonagall and Professor Dumbledore overrule him, reminding Snape that Harry is innocent until proven guilty.

When Hermione needs to raid Snape's office for Polyjuice potion ingredients, Harry tosses a firecracker into Goyle's cauldron during Potions class to create a diversion while Hermione retrieves the ingredients. Snape is unable to prove that Harry set off the firecracker, and he avoids punishment.

In the Dueling Club, Gilderoy Lockhart uses Snape as his sparring partner, though Snape easily defeats him. When Lockhart has students practice in pairs, it is Snape who halts the ensuing mayhem when students try jinxing each other and ignore Lockhart's instructions. Later, when Lockhart suggests having a student pair on the stage, Snape selects Malfoy and Harry. When Malfoy casts a serpent, Lockhart's attempt to eliminate it merely tosses the snake harmlessly into the air. Upon landing, it seems poised to strike Justin Finch-Fletchley. As Harry tries calling off the snake, Snape quickly casts a spell to dispatch it, then stares oddly at Harry; Ron and Hermione quickly escort Harry away.

After Ginny Weasley is taken into the Chamber of Secrets, Snape is among the teachers echoing Lockhart's recent boasts about his knowing the Chamber's secrets back to him, apparently in an attempt to persuade Lockhart to confront the monster. Lockhart, a fraud, returns to his office and starts packing, intending to leave Hogwarts quickly.

Prisoner of Azkaban
At the Arrival Feast, Harry notes Snape's loathing glare at the new Defence Against the Dark Arts teacher, Remus Lupin.

Draco Malfoy, claiming his injury from Buckbeak still hurts him, returns to Potions halfway through the class. Snape orders Ron to assist Draco. Harry believes a Gryffindor student would be treated quite differently if they had been 30 minutes late.

Just before Lupin's class, Snape cautions him that Neville Longbottom causes havoc with every wand stroke; Lupin counters that he hopes Longbottom will lead off his demonstration. Lupin explains to the class that the Boggart he trapped in the wardrobe will appears as its opponent's greatest fear. For Neville, that fear is Snape. The Riddikulus charm forces the Boggart to assume whatever funny guise the caster is imagining, and Lupin instructs Neville to picture Snape wearing his grandmother's clothing. Neville successfully transforms the Boggart twice, though when Snape later hears about this, he mercilessly bullies Neville in Potions.

Harry, lacking parental permission to visit Hogsmeade on a student outing, is invited by Professor Lupin to his office. While there, Professor Snape brings in a steaming potion for Lupin, then leaves. Despite Harry's warning that Snape would likely do anything to obtain Lupin's job, Lupin drinks the potion. At dinner, Harry notes how Snape intently watches Lupin, but, apart from seeming rather fatigued, Lupin shows no ill-effect from the potion.

Following fugitive Sirius Black's break-in into the castle, Professor Dumbledore orders all students to sleep in the Great Hall. Prefects stand guard while the teachers search the castle and grounds. Harry, Ron, and Hermione are still awake when Snape gives the all clear to Professor Dumbledore. Snape reminds Dumbledore about his concerns over a recent appointment Dumbledore made, but Dumbledore avers that nobody at Hogwarts would have aided Black.

Harry, arriving ten minutes late for Defence Against the Dark Arts class, is dismayed to find Professor Snape substituting for an ill Lupin. After penalizing Harry for tardiness, he continues teaching. He asks a question about werewolves and Hermione raises her hand, but Snape ignores her and Hermione starts to answer the question. However, Snape takes five house points from Gryffindor from Hermione for being "an insufferable know-it all." Hermione gets very upset at these words. Ron stands up for her and criticizes the way Snape teaches. Snape assigns Ron detention. He tells Ron that if he ever criticizes the way he teaches a class again, he will be "very sorry indeed." He also declares the class should be further along, and sets an essay on Werewolves. Upon his return, Professor Lupin cancels the assignment, much to Hermione's dismay, who apparently completed it.

Professor Snape is among the teachers staying at the school over the Christmas holiday. Throughout the Christmas dinner merriment, he remains sour looking. Dumbledore asks him if Professor Lupin has been receiving his potion.

There is another Hogsmeade weekend, only this time, Harry, using his Marauder's Map and Invisibility Cloak, intends to travel the secret passage to Honeyduke's. But Snape catches Harry on his way to the tunnel's entrance and orders him back to Gryffindor tower. Harry notices Snape inspecting the hump-backed witch statue as if he had read Harry's mind that a passage starts there. Harry returns later and follows the underground path leading to Hogsmeade. He is spotted in Hogsmeade, and rushes back to the castle where Snape, apparently alerted, catches him. Snape confiscates the Marauder's Map and commands that it reveal itself. The map, writing as Messrs. Moony, Padfoot, Wormtail, and Prongs, only insults Snape. Snape shows the map to Lupin, who claims it is merely a Zonko's Joke Shop insult scroll. He collects Harry, the map, and also Ron, who arrived to support Harry's story, and takes them out of the now clearly livid Snape's office.

During Snape's Potions final exam, Harry is doing poorly. Snape scribbles what looks like like a zero on Harry's notepad before walking away.

Snape hides under Harry's Invisibility Cloak inside the Shrieking Shack as Lupin and Sirius tell Harry, Ron, and Hermione about their days at Hogwarts. Snape, their classmate, was tricked by Sirius and nearly killed by Lupin, who was confined in the Shrieking Shack during his werewolf transformations. Harry's father, James, saved Snape by preventing him from entering the Shack. Revealing himself, Snape says he saw Sirius' name on the Marauder's Map in Lupin's office. He ignores Remus' explanations about Sirius' innocence, instead binding both him and Lupin, intending to turn them over to the Dementors at the castle. Harry, Ron, and Hermione simultaneously Disarm Snape, rendering him unconscious.

Snape awakens after Peter Pettigrew was revealed to be alive and had escaped. Snape collects the unconscious Sirius, Harry, and Hermione, who were disabled by Dementors, and also Ron, who Pettigrew jinxed, and takes them to the castle. With Sirius now captive, and the Trio in the Hospital Wing, Snape summons Cornelius Fudge to report that he captured Black. Harry awakens in the Hospital Wing and overhears Snape telling Fudge that Lupin helped Sirius break into Hogwarts and also claims that anything Harry and Hermione might say should be discounted because they were Confunded. Snape appears pleased when Fudge says Snape could receive an Order of Merlin.

When Dumbledore arrives to speak with Harry and Hermione, Snape and Fudge head off to witness the Dementors administering the "Kiss" to Sirius, only to discover that Sirius escaped. Snape, raging mad, accuses Harry of being involved, despite Madam Pomfrey's assertion that he and Hermione were always in the infirmary. As Snape angrily stalks off, Fudge comments that Snape seems unhinged.

The next day, still angry, Snape reveals to everyone at Hogwarts that Lupin is a werewolf, causing Lupin to resign his post as the Defence Against the Dark Arts instructor.

It was learned during the episode at the Shrieking Shack that Snape had been brewing the Wolfsbane potion for Lupin to retain his mind during his werewolf transformations. Snape is among the few who can successfully brew the complicated potion, a recent discovery. Snape believed, correctly, that Lupin might have missed the final dose of this potion, and was bringing it to him, when he happened to see the Marauder's Map on Lupin's desk. The Map revealed that Sirius Black was passing through the tunnel under the Whomping Willow, which spurred Snape's interference.

Goblet of Fire
When Draco Malfoy attempts to Jinx Harry, Professor Moody transforms Draco into a white ferret. Professor McGonagall sternly warns Moody that Hogwarts professors never useTransfiguration as punishment and should instead report Draco to his House Head, Professor Snape. Moody, a retired Auror, departs with Draco in tow, claiming Snape is an "old friend."

Snape seems harsher than usual on his Potions students. Apart from his resentment at being passed over yet again for the Defence Against the Dark Arts post, Snape appears to fear and despise Moody, and may be venting his resentment on the students.

It is mentioned that Snape has Harry's class researching antidotes, leaving Harry worried there will be a practical test – a student will be poisoned, and Harry worries he might be the test subject.

When Harry's name is ejected from the Goblet of Fire, he proceeds as directed to the chamber where the other Champions are waiting. Snape and the other teachers and judges join them. Igor Karkaroff and Madame Maxime are adamant that Harry somehow crossed Professor Dumbledore's Age Line that restricted underage wizards. Snape snidely observes that Harry has been crossing lines ever since his arrival at Hogwarts. He tells Karkaroff not to go blaming Dumbledore for Harry's "determination to break rules."

Harry, fed up, confronts Draco Malfoy about his anti-Harry lapel buttons. Their clashing spells deflect onto Goyle and Hermione. Snape sends Goyle, sprouting boils, to the Hospital Wing while professing that Hermione, whose front teeth have grown enormous, is fine, causing Hermione to run off crying. Harry and Ron protest Snape's unfair treatment, only to have him penalize Gryffindor House 50 points and assign Harry and Ron detention. That day's potion lecture concerns antidotes, and Snape announces they will test one. Harry is relieved when he is summoned away from class to attend the Wand Weighing ceremony, though this only intensifies Snape's resentment over Harry's increased publicity.

During Snape's antidote exam, Harry, panicked that he has yet to find a date for the Yule Ball, forgets a vital ingredient, and fails the test.

At the Yule Ball, Harry and Ron eavesdrop on Snape and Karkaroff in the rose garden. Snape is blasting the bushes apart, penalising students hiding within as Karkaroff complains that something is becoming more visibly distinct; Snape responds that Karkaroff may run if he chooses. Ron wonders how Snape and Karkaroff got on a first-name basis.

Harry has heeded Cedric Diggory's advice and had taken his Golden Egg to the Prefect's Bathroom to help decipher a clue for Second Task. While checking his Marauder's Map to make sure the hallways are clear, Harry notices Bartemius Crouch in Snape's office. Curious, Harry decides to investigate, but his foot becomes trapped in the staircase's trick step. The dropped Egg starts wailing, summoning Filch, Snape, and eventually Professor Moody to investigate the noise. Only Moody, with his magical eye, can detect Harry under his Invisibility Cloak. Snape suspects someone was in his office, which interests Moody. When Moody notices the map and thinks Snape dropped, Harry gesticulates wildly to indicate it is his. Moody quickly Summons it. Snape, recognising the Map, suspects Harry must be close by under his Invisibility Cloak. Moody claims nobody is there and comments about how quickly Snape's mind jumped to Harry. After Snape and Filch depart, Moody rescues Harry from the step.

In Potions class, the Slytherins are huddled over something, sniggering. Pansy Parkinson tosses a Witch Weekly to Hermione. Inside is Rita Skeeter's article, Harry Potter's Secret Heartache. The article suggests Hermione romantically threw over Harry for Viktor Krum and might be using love potions. Professor Snape appears and penalises Gryffindor ten points, then ten more for having Witch Weekly in class. He reads Skeeter's article aloud, inciting laughter from the Slytherins. Snape then places Harry at the table immediately facing his desk. Snape softly mutters to Harry that he knows he is stealing Boomslang skin and Gillyweed from his stores. Harry denies it, but remembers that Hermione once stole Boomslang skin to make Polyjuice potion, and that Dobby swiped the Gillyweed. Snape produces a vial containing Veritaserum, implying he may use it on Harry.

Igor Karkaroff enters the classroom, claiming Snape has been avoiding him. Harry stays after class, crouching behind his cauldron so he can listen. Karkaroff shows Snape something on his left forearm saying, "It has never been that clear, not since . . . ." Snape says they can discuss it later. When Harry is spotted, Snape and Karkarov fall silent, and Snape orders him to leave.

Sirius, who has been hiding out in a cave outside Hogsmeade, tells Harry, Hermione, and Ron it seems curious that Snape and Karkaroff were talking together. While Karkaroff was a Death Eater, Snape was never accused of being one, despite his skill in the Dark Arts. According to Sirius, Snape also hung around Evan Rosier, Wilkes, Bellatrix Black, Rodolphus Lestrange, and Avery when they were students at Hogwarts.

When Bartemius Crouch, confused and rambling, is found near the Forbidden Forest, Harry runs to Professor Dumbledore's office for help, only to find Snape blocking his path. Dumbledore appears and Harry explains the situation. Soon after Dumbledore and Harry arrive back at the scene, Moody also appears, saying Snape told him they were there.

In Dumbledore's Pensieve, Harry views Dumbledore's memories of Death Eaters' Wizengamot trials. Karkaroff attempts to lighten his own sentence by identifying other Death Eaters. He names Severus Snape, but Dumbledore claims that Snape was a double agent working against Voldemort. A bit later, while talking to Dumbledore, Harry's face appears in the Pensieve, smoothly changing into Snape's, who says, "It's coming back, Karkaroff's too". Harry asks why Dumbledore trusts Snape, but Dumbledore replies that is between him and Snape.

Upon Harry's return from the Little Hangleton graveyard, Moody steers him to his office, despite Dumbledore's having told Harry to stay put. Just as Moody reveals he is a Death Eater intending to kill Harry, Dumbledore, McGonagall, and Snape burst in, stunning Moody. Dumbledore commands Snape to bring truth serum and to fetch Winky from the kitchens. Moody transforms into a man that Winky identifies as Barty Crouch, Bartemius Crouch's son. Barty admits that he had raided Snape's potion supplies to make more Polyjuice Potion for his disguise as Mad Eye Moody.

Harry, sent to the Hospital Wing, awakens to hear Cornelius Fudge and Dumbledore arguing about Voldemort. Snape shows Fudge the Dark Mark on his left forearm, saying it is how Voldemort communicated with his Death Eaters. The mark has been growing darker recently, and it burning his arm a few hours ago proves Voldemort has returned. Fudge, disbelieving Snape, departs. Dumbledore requests that Sirius and Snape put aside their mutual dislike and work together for the Order. Snape is then sent on a mission that he and Dumbledore had previously discussed.

At the Leaving Feast, Snape is present, apparently having returned from his mission; Harry thinks he is more sour-looking than usual.

Order of the Phoenix
Harry, arriving at the Order of the Phoenix Headquarters, is very disappointed to find Snape there. Snape leaves before Fred and George can use their Extendable Ears to eavesdrop on the Order's meeting.

Immediately before Potions class, Draco Malfoy snidely comments that mentally deficient people should be confined to St. Mungo's. Neville, livid, attacks Draco, though Harry and Ron restrain him. Snape enters and promptly penalises Gryffindor 10 points for fighting. Ron wonders what prompted Neville's outburst, though Harry, knowing what happened to Neville's parents, says nothing as Dumbledore had requested. Professor Umbridge, acting Hogwarts High Inquisitor, is monitoring Snape's class. She asks how long Snape has taught at Hogwarts ("fourteen years"), and about his applying as the Defence Against the Dark Arts. Snape replies he has repeatedly been declined the post and to ask Dumbledore if she wants to know the reason. Straining to overhear, Harry ruins his potion and receives a zero.

While Harry is at Grimmauld Place for Christmas, Snape arrives and informs him he will be studying Occlumency, the art of closing one's mind from another's intrusion. Harry agrees until he discovers that Snape, not Dumbledore, will be instructing him. Sirius wants Dumbledore to teach Harry, and a verbal battle between Sirius and Snape erupts and escalates into drawn wands. Harry stands in-between, trying to prevent a duel. Only Hermione's and the entire Weasley family's timely arrival interrupts them. Snape departs, telling Harry to be his office at 6 o'clock Monday evening. Later, Hermione says Harry will be happy to stop the nightmares. Ron comments that he would rather have the nightmares.

Harry, still distrustful, begins his first Occlumency lesson with Snape. Legilimency, Snape explains, is the ability to read other's thoughts and memories. Voldemort is an expert in Legilimency, and Occlumency will help Harry block his mind. Snape removes some of his memories and deposits them into a Pensieve. Harry's first attempts to block Snape penetrating his mind fail miserably. However, Harry now recognises the hallway he has frequently dreamt about; it is the hall in the Ministry of Magic leading to the Department of Mysteries. it is the same hallway the snake attacked Mr. Weasley. Snape dismisses him, and while leaving, Harry sees Snape reinserting his memories back into his head.

Over the next few months, Harry's Occlumency lessons proceed poorly. He is unable to block Snape's probes, his scar pricklels almost continually, and he still experiences Voldemort's emotions. Ron thinks Snape may be making it easier for Voldemort, but Hermione reiterates that Dumbledore trusts Snape. Harry's hatred for Snape hinders him, though he is making some progress, and, on one brief occasion, enters Snape's mind. Harry again experiences his corridors dream, but upon reaching the door, Snape breaks his vision, seemingly concerned by what appeared in Harry's mind. Professor Trelawney's wailing in the hallway interrupts the session; Umbridge has just dismissed her.

When Snape is summoned by Umbridge during another Occlumency session, a shimmering light catches Harry's eye. Peering inside the Pensieve, he sees a young James Potter and Sirius Black at Hogwarts. They are cruelly tormenting their classmate, Severus Snape, by suspending him upside down in mid-air, exposing his dingy underwear. Lily Evans intervenes and berates James and Sirius for their deplorable behaviour. The humiliated Snape resents Lily's help and insultingly calls her a "Mudblood". Harry is appalled by his father's bullying behavior, but before considering it further, the present-day Snape yanks him from the Pensieve. Furious, Snape demands that he never reveal what he has seen to anyone, and orders him to leave, permanently ending their lessons. Later, Harry lies to Hermione, claiming Snape says he needs no more lessons.

It is mentioned that Harry performs creditably in his Potions O.W.L., perhaps because Snape is absent.

Harry envisions Sirius being tortured at the Ministry and unsuccessfully tries contacting him via the Floo network. Umbridge catches Harry and summons Snape, demanding he use truth serum on him. Snape claims she used all the Veritaserum while interrogating other students, even though only three drops is needed. When he says it will takes weeks to brew more, Umbridge places him on probation, then dismisses him. Harry, suddenly remembering that Snape is an Order of the Phoenix member, cryptically tries to warn Snape about Sirius, but Snape appears dismissive and leaves.

Following the battle at the Ministry in which Sirius was killed, Dumbledore tells Harry that Snape, a double agent for the Order, had contacted Sirius to confirm he was safe at Grimmauld Place. He then saw Harry, Hermione, and Umbridge going into the Forbidden Forest. When they failed to return, Snape alerted the Order. Dumbledore further explains that he had wanted Harry to learn Occlumency to block Voldemort from implanting visions into Harry's mind and luring him into a trap. Dumbledore believed that the old animosities between Snape and Harry, and also between Snape and Harry's father, James, could be forgotten, but admits he was wrong. Dumbledore did not tutor Harry himself because he feared Voldemort could see that their relationship was more than headmaster to student, opening them both to attack. Harry believes Snape deliberately waited too long to warn the Order about Sirus.

Harry nearly gets into a duel with Draco Malfoy, but Snape intercedes. Snape is about to penalise Gryffindor House points, but realises Gryffindor has no points left. Professor McGonagall suddenly arrives, and generously awards House points to the Gryffindor students who fought at the Ministry, then deducts the amount Snape was going to penalize Gryffindor.

Half-Blood Prince
Bellatrix Lestrange and Narcissa Malfoy arrive in Spinner's End. Narcissa, worried about a task the Dark Lord has assigned her son, Draco, seeks Severus Snape's help, though Bellatrix distrusts him. At Snape's house, his home during the summer break, Wormtail (Peter Pettigrew) serves drinks, then is dismissed while complaining bitterly about having to perform menial work. Snape fires a jinx at the bookcase where, listening from behind, Wormtail yelps and retreats.

Despite Voldemort trusting Snape, Bellatrix does not, and she fires probing questions at him. He responds that, like many Death Eaters, he did not search for the Dark Lord because he believed he was finished. Snape remained at Hogwarts after Voldemort's fall to continue spying on Dumbledore, gathering sixteen years of intelligence on Dumbledore while Bellatrix languished uselessly in Azkaban prison. Snape protected the Philosopher's Stone because it appeared that Quirrell sought it for himself. Snape ignored Voldemort's summons after his return to avoid Dumbledore's suspicion. Snape taunts Bellatrix about the Ministry fiasco, and claims the Dark Lord had ordered him to stay away to protect his position at Hogwarts. Snape has not killed Harry Potter because he would lose Dumbledore's protection and be unable to spy for Voldemort. Dumbledore's trust in him is what has made him useful to the Dark Lord.

With Bellatrix's worries seemingly overridden, Narcissa explains that Voldemort assigned Draco a difficult and probably fatal assignment. She wants Snape to protect her son. Snape, however, already knows about Draco's task, and refuses to try and change Voldemort's mind. Snape agrees that Voldemort's real intent is revenge against Narcissa's husband Lucius for his failure at the Ministry. Narcissa persuades Snape to swear an 'Unbreakable Vow to protect Draco and complete his task should he fail. Bellatrix acts as their Bonder, though apparently half-expecting Snape to somehow invalidate the Vow.

Aboard the Hogwarts Express, Harry, suspecting Draco has become a Death Eater, eavesdrops on him. Draco spots Harry and petrifies him, then stomps on his face before covering him with his Invisibility Cloak, leaving him on the train. Tonks finds Harry before the train departs for London. Harry, arriving late at the school, finds Snape waiting at the gate. Snape jeers at Tonks' new Patronus shape that she sent to the castle to alert the staff about Harry. After Tonks leaves, he penalizes Harry fifty house points for "lateness" and an additional twenty for "muggle attire."Then Snape, refusing to allow Harry to change or clean up, takes him directly into the Great Hall, where the Arrival Feast is just ending. Harry is shocked when Snape is announced as the new Defence Against the Dark Arts teacher. It had appeared that Professor Horace Slughorn, the new Potions teacher Dumbledore just recruited, was hired for that position. Harry finds Snape's Dark Arts class both illuminating and alarming, with Snape almost seeming unnaturally entranced by the subject. Snape teaches the class how to cast wordless spells, though the students are having difficulty. To demonstrate, Snape squares off against Harry, who fearing any spell Snape might cast against him, uses a verbal shield spell and then Snape asks him if he remembers that they are practicing nonverbal spells. Harry is cheeky to Snape, earning Harry a detention. The detention conflicts with one of Slughorn's "little soirées", and Slughorn prevails upon Snape to change Harry's detention time, though Snape refuses. Harry is uncertain which is worse, Slughorn's party or Snape's detention.

Harry discovers a non-verbal spell, Levicorpus, in the Half-Blood Prince's Potions book which he is using in Slughorn's class. It appears to be the same spell that Harry, once watching Snape's memories in a Pensieve, had seen his father use to humiliate Snape when they were both Hogwarts students.

When Katie Bell is nearly killed after touching a cursed necklace, Professor McGonagall has it taken to Professor Snape for examination. Later, Professor Dumbledore tells Harry that Snape had done all he can to help Katie, explaining that Snape has more experience with Dark magic than Madam Pomfrey.

At Slughorn's Christmas party. Slughorn mentions to Snape that Harry seems a natural at Potions, like his mother, though Snape has a different opinion. Argus Filch suddenly appears, dragging Draco Malfoy, who was "skulking" about in the halls. Slughorn assumes Draco was gatecrashing the party, while Draco hardly seems pleased that Slughorn allows him to stay. Soon after, Snape and Draco, leave together. Following under his Invisibility Cloak, Harry eavesdrops on their conversation. Snape probes Draco's mind for details about Katie Bell, but Draco blocks him, apparently having been tutored in Occlumency by his aunt, Bellatrix Lestrange. Snape says he knows about Draco's mission and has taken an Unbreakable Vow to help him. Draco, angered at the thought that he could need help, storms off.

Harry, believing Snape and Draco are working for Voldemort, discusses his suspicions with Ron, Mr. Weasley, Remus Lupin, and Hermione. Everyone discounts Harry's opinion, saying they have absolute faith in Dumbledore and his trust for Snape; it is more likely that Snape wants to learn what Draco's mission is so he can inform Dumbledore. Despite Snape's costing him his job at Hogwarts by revealing his being a werewolf, Lupin claims Snape had always perfectly brewed his werewolf potion. Snape could have done far more damage if he had wanted. At their next lesson, Harry reports his suspicions to Dumbledore. Dumbledore thanks him, but, for confidential reasons, states he absolutely trusts Snape.

Snape is briefly mentioned during Slughorn's Potions class. Harry must create an antidote for several different poisons and finds nothing in the Half-Blood Prince's textbook about them except a notation, "Just shove a Bezoar down their throat." Remembering Snape's comment in his first-ever Potions class, Harry grabs a bezoar from the supply closet, and shows that to Slughorn as his finished potion.

Hagrid mentions overhearing an angry-sounding exchange between Snape and Professor Dumbledore. Snape expressed second thoughts about something he had promised Dumbledore he would do. Something was also said about Snape's investigations into Slytherin house, which Hagrid assumed was about the Cursed necklace. Filch's sudden arrival interrupted their conversation.

Harry believes Draco is using the Room of Requirement to perform his secret task. Just before class, Harry attempts to enter the Room, but is unable to make the door appear. Snape penalizes Gryffindor ten points when Harry arrives late. Seamus Finnigan asks Snape about the difference between ghosts and Inferi, as a story in the Daily Prophet mentioned Inferi; Professor Snape says the story actually was about one Mundungus Fletcher, who was arrested for impersonating an Inferius. After class, Ron's girlfriend, Lavender, starts dissing Snape, irritating Ron rather than amusing him, and he and Harry duck into a bathroom to avoid her.

When Harry and Dumbledore view Slughorn's memory about Tom Riddle, Dumbledore explains that he injured his hand destroying Voldemort's Horcrux. Only his own reflexes and Snape's timely intervention contained the damage.

Harry's Marauder's Map shows that Draco is in Moaning Myrtle's bathroom, one floor below. Harry investigates but is spotted by Malfoy, who casts the Cruciatus curse; Harry counters using the Sectumsempra spell from the Half-Blood Prince's book without knowing its effects. Draco is severely slashed, his blood spilling everywhere, causing Moaning Myrtle to fly off screaming; Professor Snape responds swiftly and saves Draco, rushing him to the Hospital Wing. Returning, Snape demands to know whence Harry learned the spell, and despite Harry's attempts at occlumency, Snape apparently gleans some information that Harry's potions book is the source. Snape demands to see his textbooks. Harry instead gets Ron's Potions textbook, then hides the Half-Blood Prince's book in the Room of Requirement before returning to Snape.

Snape, skeptical this is actually Harry's book, particularly since it is signed "Roonil Wazlib", assigns Harry detention (with Professor McGonagall's concurrence) every Saturday until school ends. Reporting to Snape's office, Harry is assigned to copying old detention files, with Snape suggesting he start with ones detailing his father's misbehaviour. Fearing Snape might confiscate his Potions textbook, Harry hides it in the Room of Requirement. As a result, Harry's Potions work now suffers, though Slughorn attributes it to his new romantic interest in Ginny.

Professor Trelawney happens to mention to Harry that it was Snape who overheard the prophecy foretelling Voldemort's nemesis, and he carried this information to Voldemort. Harry angrily confronts Dumbledore, but Dumbledore avers that he trusts Snape. He seems about to explain why he does, but quickly changes the subject by saying he has located another Horcrux.

Harry and Dumbledore retrieve the Horcrux, but the Headmaster is left greatly weakened by the effort, and Harry assists him back to the castle. Landing atop the Astronomy tower, Dumbledore tells Harry to fetch Severus, but Draco unexpectedly appears and disarms Dumbledore. Dumbledore offers Draco protection if he switches sides, but four Death Eaters intervene. Snape also bursts onto the scene, and Dumbledore seems to be pleading with him. Snape kills Dumbledore, then departs with the Death Eaters and Draco. Harry, who was petrified for his protection under his Invisibility Cloak by Dumbledore, is freed by Dumbledore's death. Harry Stuns a Death Eater and chases Snape, firing spells at him. Snape, easily blocking every curse, criticizes Harry's Occlumency skills that leave his mind open to opponents. Harry is stunned when Snape reveals he is the Half-Blood Prince who once owned Harry's Potions book. Snape prevents the other Death Eaters from attacking Harry, saying that the Dark Lord wants him for himself; he then escapes with Draco and the other Death Eaters.

Harry learns that during the battle Snape was allowed to enter the tower. When he returned, Order members never suspected Dumbledore had just been killed, believing Snape was only fetching Draco. Harry reveals that Dumbledore had trusted Snape because after Snape carried the prophecy to Voldemort, he later returned to Dumbledore, claiming remorse.

Hermione's research reveals that Snape's mother was a witch, named Eileen Prince, his father, Tobias Snape, was a Muggle, hence Snape's self-imposed nickname, the Half-Blood Prince. Harry is upset that he had Snape's unwitting help, through his old Potions book, all year. He wonders also at the similarity between Snape's half-blood ancestry and Voldemort's, and wonders how Dumbledore could have missed it.

Deathly Hallows
Snape and a Death Eater named Yaxley enter Malfoy Manor, Voldemort's new headquarters. At the council table, Snape is placed at Voldemort's right hand side. Yaxley, sitting in the middle, reports that Harry Potter will be moved to an Order safe house on Harry's 17th birthday, though Snape disputes this. His information, "from the same place as before," indicates the move will occur earlier and by Order members, as the Order no longer trusts the Ministry. Snape does not flinch under Voldemort's intense gaze, though some of the Death Eaters present look away. Voldemort decides that the attack on Harry will take place according to Snape's information.

During the escape from Privet Drive, George Weasley, disguised as Harry, has his ear severed by Snape, using the Sectumsempra spell.

While hiding out in Grimmauld place, Harry, Ron, and Hermione read in the Daily Prophet that Snape had been appointed Headmaster of Hogwarts. Hermione realizes that Phineas Nigellus Black's portrait is now a conduit to Snape, as his other portrait hangs in the Headmaster's office. To prevent Phineas from spying on them, she stuffs his picture into her small beaded bag carrying their traveling gear.

One night, while traveling the countryside, Harry, Ron, and Hermione happen to overhear a conversation about three Hogwarts students, including Ginny Weasley, having broken into the Headmaster's office and attempting to steal the Sword of Gryffindor. A Goblin in the group says that shortly after, the Sword was transferred to Gringotts Bank for safekeeping, though that Sword is actually a fake. The three students involved reportedly were "cruelly punished," but when Harry and Hermione consult Phineas Nigellus' portrait, he reports the students were merely sent to Hagrid, who set them to work in the Forbidden Forest.

Harry, re-entering Hogwarts, heads to the Ravenclaw common room to see the sculpture of Rowena Ravenclaw wearing her lost Diadem. Alecto Carrow spots him and touches her Dark Mark to alert Voldemort that Harry has been found. Professor McGonagall, helping Harry escape, runs into Snape in the hall. Snape is searching for Harry who is hidden under his Invisibility Cloak. Snape seems to be using Legilimency to locate him. McGonagall and Snape duel, but when the other House Heads arrive, Snape runs and leaps out a window. Harry believes he must have fallen to his death, but sees a large, bat-like shape flying over the castle wall — Snape has escaped.

Harry, Hermione, and Ron travel through the tunnel under the Whomping Willow to the Shack where Voldemort is. There, they witness a confrontation between Snape and Voldemort. Snape asks permission to enter Hogwarts and bring Harry out. Voldemort refuses, saying he is disappointed by the Elder Wand's performance. He believes the Wand answers not to him but to Snape, who killed Dumbledore, the Wand's previous owner. Saying he regrets the necessity, Voldemort orders Nagini to kill Snape, then leaves.

Harry rushes to Snape's side as soon as Voldemort leaves. Snape offers Harry his memories, which Harry collects in Hermione's crystal vial, and, gazing into Harry's eyes, so much like his mother's, dies.

Harry enters the headmaster's office and pours Snape's memories into the Pensieve. Harry views snippets of Snape's life:

Snape sees Lily Evans, about ten-years-old, experimenting with magic. He tells her she is a witch, and that he is a wizard. Lily's sister, Petunia, is clearly frightened by her sister performing magic, while Lily seems affronted Snape called her a witch. Snape tells Lily things about the Wizarding world. Later still, we see Snape watching Lily and her family as they put Lily on board the Hogwarts Express for her first term at Hogwarts. Petunia is telling Lily that she's a freak, that Lily and that Snape boy are being sent to a school for freaks. Lily says that she had seen Dumbledore's reply to Petunia's letter, and that he had been very kind. When Petunia demands to know how she had seen that letter, it was private, Lily indicates that Snape had helped. Petunia flounces off to join her parents. We then see Severus on board the train, looking for Lily. He finds her in a compartment with James Potter and some other first-year students, including Sirius Black. Snape says he hopes Lily will be placed in Slytherin; James is adamant that he wants to go to Gryffindor. When James insults Snape, Lily leaves to find a different compartment, and Snape follows; James tries to trip Severus as he passes.

At the Sorting ceremony, Lily is placed in Gryffindor, along with Sirius Black, James Potter, Peter Pettigrew, and Remus Lupin. Snape is sorted into Slytherin, where he is greeted by Lucius Malfoy.

Snape and Lily are seen strolling across a courtyard, quarreling. Snape wonders what has happened to their friendship. Lily responds they are still friends, but she detests his friends, most notably Avery and Mulciber. Snape reminds Lily about the trouble James and his friends get into, and is heartened when Lily dismisses James as an "arrogant toe-rag."

Harry witnesses a scene he saw some years earlier, when James, along with Sirius, tormented Snape. Not wishing to revisit this scene, Harry keeps his distance. The memory ends with Snape calling Lily a Mudblood, and reforms in front of the Fat Lady. Lily says that she had heard that Snape would stay outside the entrance to the Gryffindor Common Room all night, unless she came out to speak with him. Despite his obvious remorse, and his heartfelt apologies, Lily will not forgive Snape the insult, and tells him that he should go to his Death Eater friends.

We now see Snape meeting in secret with Dumbledore. Snape says he does not carry a message from Voldemort, but is there to plead on his own behalf. He had carried Trelawney's prediction to Voldemort, and Voldemort, having decided that the prophecy referred to Harry Potter, was now planning to kill not only Harry, but also Lily and James. Snape pleads with Dumbledore to save Lily from Voldemort. Dumbledore is disgusted that Snape only wants Lily saved, not caring about her husband or child. Taken aback, Snape pleads for them as well, saying that in return for their safety he would do anything.

Next, Snape is in Dumbledore's office, plainly grief-stricken. Snape demands of Dumbledore why he had not kept Lily and her family safe. Dumbledore tells him that they had put their trust in the wrong man, just as Snape had in trusting Voldemort to spare Lily's life. Dumbledore reveals that Harry had survived, and that if Snape had truly loved Lily, he would help Dumbledore protect her son when Voldemort returns. Snape reluctantly agrees, but says that Dumbledore must never tell anyone that he is protecting James Potter's son.

Snape, apparently during Harry's first year at Hogwarts, is complaining fiercely to Dumbledore about Harry, and how he is a troublemaker like his father. Dumbledore responds mildly that no other teacher is complaining, and asks Snape to keep an eye on Quirrell.

As students leave the Yule Ball, Snape tells Dumbledore that the Dark Mark on his arm is growing darker, as is Karkaroff's, and that Karkaroff plans on fleeing if the Mark burns him. Dumbledore asks if Snape has similar plans, and Snape angrily retorts he is no coward. Dumbledore remarks, almost off-handedly, that perhaps the students are Sorted into their Houses too early; Snape seems quite taken aback by this.

We now see Snape in Dumbledore's office again. Dumbledore is semiconscious, his blackened right hand dangling over the edge of his desk. Snape, pointing his wand at Dumbledore's wrist, is muttering incantations while pouring a golden liquid down Dumbledore's throat. When Dumbledore returns to himself, Snape asks why Dumbledore had even tried on the ring, and Dumbledore says he was a fool. We see Marvolo Gaunt's ring on the table, broken, beside the Sword of Gryffindor. Snape tells Dumbledore that the curse was extraordinarily powerful, and that while he has contained it for the moment, it will eventually kill Dumbledore; he says that Dumbledore has, at most, another year of life. Dumbledore says that this makes things much easier to decide, and starts discussing Voldemort's apparent plan to have the Malfoy boy kill him, Dumbledore. Snape says that the attempt is not expected to succeed, but instead to further punish and disgrace the Malfoy family. Dumbledore correctly guesses that Snape has been given the job of killing Dumbledore should Draco fail, as Voldemort expects that Hogwarts will be fully under his control and he will no longer need a spy there. Dumbledore asks that Snape agree to watch over his school, and be the one to kill him, both to spare Draco's soul and to grant Dumbledore some dignity in death, sparing him from the malicious pleasures of Fenrir Greyback and Bellatrix Lestrange. Snape reluctantly agrees.

In the scene that Hagrid had partially overheard the year before, we now see Snape and Dumbledore walking in the castle grounds. Challenged as to what he is doing with Harry, Dumbledore says he is giving Harry information he will need, while he still can. Snape asks why he is not privy to that information as well, to which Dumbledore says he does not like to keep all his secrets in one basket. Snape appears to be angered by this, saying that his job as double agent is extremely dangerous, and he is at least as trustworthy as Harry. When Dumbledore tries to explain the next steps of his plan, Snape threatens a change of heart about killing Dumbledore when the time comes. Dumbledore reminds him of his word, and suggests that he keep an eye on Draco. When Snape still seems rebellious, Dumbledore wearily makes an appointment for later that night in his office.

Dumbledore, later, explains that Harry must not know what he has to do until the final moment. That moment will be the time when Voldemort, instead of letting his snake, Nagini, run free, he keeps her confined within a protective spell. At that time, Snape must tell Harry that Harry is an accidental seventh Horcrux, inadvertently created at his mother's death, and that he must die in order that Voldemort would be vulnerable to death. Snape feels tricked, as he had worked so hard to protect Lily's son, only to have him destined to die at Voldemort's hand. Asked if Snape has grown to care for Harry after all, Snape casts his Patronus. It is in the shape of a silver-white doe, indicating to Dumbledore that Snape is still in love with Lily, fifteen years after her death.

We learn that it was Dumbledore's portrait that ordered Snape to give Voldemort the correct time for Harry's departure from Privet Drive. Dumbledore suggests using seven Harry Potters headed for seven safe houses, and instructs Snape to plant that idea in Mundungus Fletcher's mind to pass to the Order of the Phoenix. During the actual departure from Privet Drive, we see that Snape was attempting to jinx the Death Eater drawing a bead on Remus Lupin, and air currents had caused them both to miss, resulting in Snape's spell severing George Weasley's ear.

Snape is in Sirius' old room at Grimmauld Place. He takes the second page of a letter Lily wrote, and the portion of a photograph containing her image, then leaves with them.

Finally, Snape is seen speaking with Phineas Nigellus Black's portrait. Phineas reports that Harry is in the Forest of Dean, and Snape retrieves the Sword of Gryffindor hidden behind Dumbledore's portrait, and departs with it.

Snape is not seen again, but in the epilogue, we learn that Harry has named his second son Albus Severus, after two Headmasters, and one of them was not only a Slytherin but possibly the bravest man Harry had ever known. In post-publication interviews, the author has revealed that Snape's portrait did not appear in the Headmaster's office at his death, as he had abandoned his post. Later, Harry successfully campaigned to have it placed there.

Strengths
Snape is an exceptionally intelligent and magically potent wizard. As a student, he excelled in Potions, revising many standard formulas that made brewing them easier and faster. It was said he knew more Spells, Hexes, and Jinxes in his first year at Hogwarts than most seventh-year students, and had invented many new ones. In addition to being a respected Potions expert, Snape is adept in defensive arts and highly skilled in Occlumency and Legilimency, skills that made him a valuable ally, but also a dangerous enemy. Dumbledore utilized these talents by having Snape infiltrate and spy on Death Eaters, knowing Voldemort would be unable to read Snape's mind; however, these same abilities also ideally allowed Snape to act as a double agent, as Dumbledore would also likely be unable to penetrate Snape's thoughts. Snape's persuasive abilities, including Occlumency and Legilimency, allowed him to maintain an ambiguous facade, leaving his true loyalty unknown until Book 7's conclusion. Throughout the series, however, Dumbledore steadfastly defended Snape's loyalty, both to him and the Order of the Phoenix, though he never explained the reason behind his trust.

Though Snape maintained few close relationships in his lifetime, he was intensely loyal to his allies. Unlike Voldemort, Snape possessed the ability to love, though his early proclivity for the Dark Arts and his association with certain Slytherin students, future Death Eaters, destroyed his only chance at a lasting relationship. Despite being able to love, Snape was never one to wear his heart on his sleeve and rarely exhibited any emotion other than annoyed disdain. However, it was this trait, along with his Occlumency skills, that allowed him to uphold his tenuous double-agent role, simultaneously claiming both Voldemort's and Dumbledore's confidence. Ironically, the dual identity he carried so well throughout the series could easily have concealed that he was actually loyal to no one, his neutral cover so convincing that he was positioned to align himself with either winning side, with neither the wiser. Only after Harry views Snape's memories in the Pensieve are his true fidelity and motives revealed.

Weaknesses
Snape possesses a dark, moody personality, and rarely takes the initiative to create friendships or establish personal alliances, apparently preferring solitude and mostly relying upon himself. At best he is cordial to his superiors and tolerates his peers. Only Albus Dumbledore and Professor McGonagall seem to be afforded any true esteem. Others describe Snape as unattractive, mainly with regard to his personal grooming, particularly his hair, which is described as oily. As an instructor, he favours his own Slytherin House students, capriciously punishing others, particularly Harry and many Gryffindors. This is usually for minor infractions or incidents initiated by Slytherin students, who usually escape punishment for their role in the proceedings. Snape is also unable to forget or forgive past hurts or grudges, and seems unable to look past any preconceived notions.

An only child, Snape experienced a traumatic childhood, suffering under an abusive Muggle father who resented and mistreated his witch mother. This left Snape emotionally battered, shy, insecure, and longing for some place to belong. He usually found solace only in solitude and his magical studies at Hogwarts, where he was sorted into Slytherin House. Though Snape seemed suited to Slytherin, Dumbledore, noting Snape's character many years later, suggests that students are perhaps sorted too soon, indicating his belief that Snape could have fared better in another House.

Though Snape was a magically proficient student destined to become a powerful wizard, he was unable to defend himself against classmates James Potter's and Sirius Black's merciless bullying. As a result, Snape unfairly transferred his long-held resentment and hatred onto James' son, Harry, often arbitrarily punishing Harry or singling him out for ridicule in his class. Snape becomes particularly incensed after Harry, not knowing Snape's true motives, calls him a coward as Snape flees Hogwarts with the other Death Eaters in Book 6.

Although Lily Potter was Snape's only true friend during their youth, he was unable to forgo his attraction to the Dark Arts or give up his unsavory Slytherin comrades that she strongly disliked. Never having been accepted as a peer before, his new-found companions became too strong an allure for him to heed Lily's request to abandon them. Snape inexplicably turned against Lily when she attempted to defend him during one of James and Sirius' cruel pranks, forever ending any opportunity for a more meaningful and lasting relationship with her.

Without doubt, Snape risked his life by defecting from Voldemort's service to instead serve Dumbledore. However, his actions, at least initially, were driven by selfish motives, seeking Dumbledore's protection for someone the Dark Lord had marked for death. In return, Dumbledore demanded Snape's complete loyalty and employed him as his double agent, at great peril to Snape's life. Snape agreed to Dumbledore's terms, but his goal was always to protect Lily Potter, not fight the Dark Lord to save the Wizarding world. After Voldemort murdered Lily, Snape sought revenge, and secretly protected Harry and his mission to destroy the Dark Lord. It is unknown if Snape would have turned against Voldemort had the Dark Lord never targeted the Potters, but the reader suspects not.

Relationships with Other Characters
An apparent loner with no close friends, Snape mostly keeps his own company. Throughout the series, Snape seems uniformly bitter and pernicious. While he can work and cooperate with allies who either serve Voldemort or who oppose him, Snape seems unable to actually care about anyone. Every interaction Snape has with Harry, his other students, and even at times other Hogwarts staff members, sometimes seems acrimonious and occasionally infused with venom. The only exceptions are Argus Filch, who he trusts enough to bind the wound "Fluffy" inflicted on him in Harry Potter and the Philosopher's Stone, Draco Malfoy, who he always treats with marked preference and leniency, and Headmaster Albus Dumbledore. His relationship with Professor McGonagall had always appeared cordial, though cold, until Snape became Headmaster. Snape's dealings with Voldemort's supporters, with the possible exceptions of Narcissa Malfoy and Voldemort himself, mostly seem similarly toxic. While we could speculate that Snape's consideration for Narcissa Malfoy springs from a hidden liking for her son, Draco, that remains questionable. Knowing that the Malfoy family is rich, influential, and staunch Voldemort supporters, Snape could be cultivating their favor through their son, though this seemingly changes after Lucius earns the Dark Lord's wrath. However, as Snape was working as a double agent for Dumbledore, he may also have been fostering an avenue through the Malfoys to the Dark Lord. The tone of Snape's interactions with both Dumbledore and Voldemort, however, seems somewhat fueled by the power that he and they, separately, wield with one each other.

Harry Potter
Even though Snape's relationship with Harry is important to the overall story, it is never his most significant. It is, however, the first that we are able to observe in depth. From Harry's arrival at Hogwarts, Snape's reaction to him seems illogically hostile. It first appears that Snape mainly resents Harry for his celebrity, but it is gradually learned that his negative feelings run much deeper and actually predate Harry's birth, extending as far back to when Snape attended Hogwarts with Harry's father, James, and also Sirius Black, Harry's godfather. James and Sirius mercilessly bullied Snape at school. And though Snape had always deeply loved Harry's mother, Lily, his affections for her never extended to her only child. Despite his personal feelings, Snape secretly protected Harry from Voldemort after Dumbledore extracted his promise to do so, though no one, other than those two, knew about this. Throughout the story, Harry resents, and later deeply loathes, Snape, believing him responsible for his parents' deaths and the later murder of Dumbledore. It is only after learning the truth behind Snape's actions that Harry must reconcile his long-held hatred against his former Potions master, which he apparently does as he will name his second son Albus Severus.

Albus Dumbledore
This was probably Snape's closest and longest lasting-relationship, though it was occasionally fraught with conflict and rancor. Dumbledore first knew Snape when he entered Hogwarts as a student. Young Severus was exceptionally intelligent and magically talented, though there appeared to be no notable relationship between Headmaster and student until Snape discovered that Remus Lupin, also a student then, was a werewolf. Dumbledore made Snape swear never to reveal this secret to the other students. Snape apparently honored this promise while he remained a student, and long after, though reluctantly – he attempts to get the Defence Against the Dark Arts class to recognize it on their own, and finally pushed beyond his limits, he "accidentally" lets the information slip out to his House.

After becoming a Death Eater during Voldemort's earlier reign of terror, Snape defected the Dark Lord's service to seek Dumbledore's help in protecting Lily Potter after Voldemort targeted her and her family for death, though it was Snape's actions, relaying a prophecy to Voldemort, that helped placed the Potters in danger. Dumbledore was unable to save James and Lily, and following Voldemort's demise, he offered Snape a safe sanctuary at Hogwarts, though this was probably an unpopular decision among the faculty and staff. In exchange for his help, Dumbledore had demanded Snape's promise to serve as his double agent and, believing Voldemort would one day return, to protect Harry Potter. Snape agreed, and continued in this role until his death.

Throughout the years, the two men's relationship with one another gradually changed, and Snape became Dumbledore's closest confidant and adviser, though it had appeared to readers that McGonagall held this position. While Snape was never particularly friendly with his Hogwarts co-workers, and was generally disliked by most Hogwarts students, his extreme competence in teaching Potions may have eventually overridden any objections to Dumbledore's appointing him. And while Dumbledore knew Snape would make a valuable spy against Voldemort and his Death Eaters, as well be as an excellent Potions teacher, he may have given Snape a second chance for other reasons. Dumbledore truly deplored Snape's Death Eater involvement, but Dumbledore himself had once been seduced by magic's Dark side, causing him to form a brief alliance with the evil wizard, Gellert Grindelwald. Though he finally defeated Grindelwald in a duel, Dumbledore realized that his own early failures had caused much tragedy, and this may have tempered his harsh judgment regarding Snape's misdeeds. Up until the series' end, Harry always remained convinced that Snape still served Voldemort, while Dumbledore never doubted Snape's loyalty to him (Dumbledore). And though Snape was eternally grateful to Dumbledore, and despite his disliking Harry Potter, he was deeply critical and angered upon learning that Dumbledore had been protecting Harry only to groom him as a weapon against Voldemort, knowing the boy was destined to die. Despite his strong objections, however, Snape understood Dumbledore's reasoning behind it.

Despite any underlying discord, a strong bond existed between the two men, and Snape never wavered in his loyalty or service to Dumbledore. Unfortunately, this devotion exacted a high emotional price for Snape, forcing him to honor his promise to carry out Dumbledore's final orders to help defeat Lord Voldemort.

Lord Voldemort
There is probably no person that Snape despised more than Lord Voldemort, though Snape was once his ardent and loyal follower. Snape was never inherently wicked, but his early attraction to Dark magic drew him to Voldemort. It is never entirely understood why Snape chose a Dark path, though it may have been that having found acceptance and fellowship within Slytherin House, he passively followed his Slytherin classmates into Voldemort's service. Alternatively, he might have actively chosen it, irresistibly drawn to something seemingly grandiose and important to which he could attach himself. At such an impressionable age, Snape may have been unable to fully comprehend Voldemort's evilness, though his own Dark nature played a significant factor, and he was ultimately responsible for his own decisions and wrongdoing. It was only after Voldemort targeted, and later murdered, someone Snape cared deeply about, despite Snape's then devoted servitude to him, that he turned against the Dark Lord and secretly aligned himself with Dumbledore and the Order of the Phoenix.

After Voldemort's resurrection and rise to power, Snape apparently returns to his service, as seemingly devoted as before. While readers never know Snape's true loyalties until the final book, Snape never forgave Voldemort for Lily's murder. The Dark Lord, however, always seemed confident regarding Snape's loyalty to him, perhaps discounting Snape's ability to truly love and also underestimating his Occlumency skills that effectively concealed his true thoughts from Voldemort's intense mental probes. Voldemort proved once again that he valued his minions only while they were useful. Without hesitation, he ordered Snape's death, convinced it would fulfill his plan to command the Elder Wand that he mistakenly believed had fallen under Snape's control. Though Snape did not witness Voldemort's final downfall, his actions, before and after Dumbledore's demise, aided Harry's efforts to defeat the Dark Lord.

James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew
James, Remus, Sirius, and Peter were Gryffindor students together at Hogwarts. Anointing themselves the "Marauders", all but Peter, also known as "Wormtail", were magically proficient far beyond their years. Pettigrew, who tagged after the other three, relied heavily on the other three for magical help, also becoming an Animagus solely due to their aid. James and Sirius took a particular dislike to their Slytherin classmate, Severus Snape, bullying him frequently, mostly for their own amusement. Although Lupin never participated in this activity, Snape equally despised him, initially because Lupin did nothing to stop James and Sirius from bullying him. This animosity increased after Snape discovered Lupin was a werewolf, a secret Dumbledore later made Snape swear never to reveal to other Hogwarts students. Snape never forgave James or Sirius for their cruelty, though he was far from being an exemplary person himself. Snape despised James even after he saved Snape from Sirius' potentially fatal prank, always believing James intervened solely to protect himself against being punished.

When Lupin was hired as the Defence Against the Dark Arts teacher in Harry's third year, Snape deeply resented him, though he apparently disliked anyone holding the position that he had long coveted but was continually denied. Despite this, Lupin always treated Snape with genuine respect, perhaps regretting that as a Hogwarts prefect, he had done little to curb James and Sirius' earlier bad behaviour towards Snape. Even after Snape revealed to Hogwarts students (and their parents) that Lupin was a werewolf, forcing Lupin to resign, Lupin still treated him respectfully, later telling Harry that Snape could have caused far worse damage to him and that while he was teaching at Hogwarts, Snape had always perfectly prepared his Wolfsbane Potion.

Snape had even less regard for Peter Pettigrew, a cowardly, weak wizard who - as well as being part of the gang that tormented him in his youth - later betrayed James and Lily Potter to Voldemort and framed Sirius Black for his own faked murder. Snape interacts with Pettigrew only by Voldemort's command, hiding Pettigrew at his summer home in Spinner's End, in book 6, presumably under instruction to closely watch him for the Dark Lord. He treats Pettigrew with disdain, and uses him as a servant.

Sirius Black was one of the few people Snape truly loathed. Sirius nearly cost Snape his life by urging him to investigate the mystery inside the Shrieking Shack during their Hogwarts school days. That mystery was Remus Lupin, who was confined there during his werewolf transformations. Snape likely would have been killed without James' intervention, preventing Snape's entering the Shack during a full moon. Snape never forgave Sirius for his potentially deadly trick, nor did Sirius ever show any remorse for his actions, and their mutual hatred permanently carried over into their adult lives. Sirius, of course, knew about Snape's involvement with Voldemort and other Death Eaters and how that association contributed to James and Lily Potter's deaths, further intensifying his hatred towards Snape. Despite their turbulent history, Snape and Sirius were able to somewhat subdue their mutual animosity at Dumbledore's request, to work together in the war against Voldemort. When Harry believed Sirius was in danger, Snape did warn the Order, though Harry always believed Snape deliberately delayed and was therefore partially responsible for Sirius' fate, perhaps overlooking Sirius' own reckless tendencies.

Lily Evans Potter
Lily Potter (née Evans) was the first character in the series that Snape knew, dating back to before their starting Hogwarts together. Snape, being a Half-blood, knew from an early age that he was a wizard, while Lily, a Muggle-born witch, was unable to understand her burgeoning magical powers. Snape explained much about the Wizarding world to her and that her sister Petunia's jealousy was over Lily being magical, while she was not. The two soon became close friends.

At Hogwarts, to Snape's disappointment, he and Lily were sorted into separate Houses, he into Slytherin, and she into Gryffindor. Initially, they remained close friends, and when Snape became a favorite target for James Potter and Sirius Black, also Gryffindors, to bully and torment, Lily defended him. Their once close friendship became strained, however, as Snape grew increasingly attracted to the Dark Arts and made friends with the more unsavory Slytherin students (and future Death Eaters). Their relationship finally ended over an incident involving James and Sirius, when Snape, upset and humiliated, apparently resented Lily's intervention on his behalf and aimed a derogatory comment at her. This caused Lily to permanently end their friendship despite his repeated apologies, and she eventually married James Potter, later giving birth to Harry.

Lily was the only person Snape had ever deeply cared for, and while the relationship's exact nature and Lily's true feelings for him are unknown, Snape was devastated by her death, never fully recovering. Snape's actions, learned about later in the series, were mostly driven by his love for her. Dumbledore seized upon that to secure Snape's help in protecting Harry and to combat Voldemort.

Snape's relationships with other characters is discussed in greater detail in the Greater Picture section of this article.

Analysis
Snape's actions throughout the series have shown service to each of the opposing sides. Both Dumbledore and Voldemort believe Snape is only loyal to them, allowing him to work as a double agent. Not only is it unknown until very near the end of the final book which side he is really on, but there is no concrete evidence until then that he has actually chosen one. He has made strong claims, which Dumbledore trusts, to oppose Lord Voldemort's cruelty, but hatred exists between himself and many Order of the Phoenix members. Though seemingly fearing a world under Voldemort's domination, he would appear to have equally little place in one where the Order is victorious. There is little reason to believe he has an interest in either side winning, and he may even prefer being able to exert influence on, and gain favours from, both.

Snape exhibits both good and evil qualities, making him the series' only anti-hero. Snape possesses a nasty demeanour, and is especially retaliatory to those who hurt him (James, Sirius, Snape Sr.) However, Snape's seeming cruelty may have resulted from a terrible childhood and early youth. When Harry delved into Snape's early memories, there was nothing good to be seen, only an abusive father, a victimized mother, derisive classmates, and a cruel James Potter and Sirius Black. While the series does little to emphasize Snape's good qualities, it is implied, at least until the end of Harry Potter and the Half-Blood Prince, that he would protect Order of the Phoenix members with his life. He has saved Harry's life on more than one occasion, though it might take a particularly observant reader to see that. Though he treats students badly and is seemingly indifferent to their feelings or situations, he wants them to learn valuable lessons.

During the series, we see these contradictions in Snape's behaviour. He seems motivated by his hatred for Harry and, occasionally to some extent, Dumbledore. We can easily believe, like Harry, that Snape is attempting to eliminate Harry in Harry Potter and the Philosopher's Stone. Snape's consistently sabotaging Harry's Potions coursework throughout the year is clearly going to be something of a recurring story element throughout the series. Yet by that book's end, Snape acted to save Harry's life in his first Quidditch match. In Harry Potter and the Prisoner of Azkaban, we are as aware as Harry that Snape coveted Remus Lupin's teaching post, and that Snape distrusts Lupin; yet, Snape had repeatedly brewed a very tricky Wolfsbane potion, flawlessly, fully aware that any minor error would have eliminated Lupin from the school forever, without provable intent on Snape's part – "Anyone can make a mistake, Headmaster, surely you don't think I would have deliberately done anything to risk a student's death from a werewolf bite?" And as late as the final book's mid-section, when we hear that Ginny Weasley, Luna Lovegood, and Neville Longbottom had been "punished cruelly" by being sent to help Hagrid, when Snape knows precisely where Hagrid's sympathies lie, we are left wondering whether Snape deliberately minimized the punishment he was meting out to protect the students.

That Snape's mother's surname was Prince, and that he is a half-blood, hints broadly at the title character's identity in the sixth book, Harry Potter and the Half-Blood Prince. As Harry spends much time trying to uncover who this character is, prematurely revealing his identity would constitute a plot spoiler.

Harry Potter and the Deathly Hallows (The Prince's Tale)
The memories Snape reveals to Harry serve two purposes. The first set, up to the deaths of Harry's parents, seem to explain Snape's feelings, and provide a basis for his later actions. Snape, who first met Lily Evans at age 9 or 10, had revealed to her that she was a witch and he was a wizard, and introduced her to the Wizarding world. He had also defended her against her Muggle sister, Petunia, as Lily prepared for her first year at Hogwarts. They became close friends, a friendship that was eventually strained to destruction by Snape's association with darker Slytherin students. Despite their friendship's demise, Snape continued loving Lily, and he had agreed to do anything in exchange for Dumbledore's promise to save Lily, and her family, from Voldemort. When the story opens, Snape had kept this promise for eleven years, starting when he first turned informant against Voldemort, and continued to keep it throughout the series, even beyond Dumbledore's death, protecting Harry against Voldemort and his allies.

After James and Lily's deaths, Snape's memories, while still reinforcing our understanding of Snape's unrequited love for Lily, also show Dumbledore and Snape working together to protect Harry and mold him into the weapon that eventually destroys Voldemort. Dumbledore, knowing he had little time left and that Voldemort had charged Draco with killing him, orchestrated his own demise at Snape's hands, telling Snape it was to protect Draco's soul, and to allow Dumbledore to retain some dignity in death. We also learn that Harry has become an unexpected seventh Horcrux, and that Snape must somehow have Voldemort kill Harry in order to destroy it. We learn, in particular, that Dumbledore had set large plans in motion, and that Snape, much to his own dismay, was merely a cog in Dumbledore's machinations. Snape is particularly dismayed that, having worked so long and so diligently to protect Harry, they must now arrange his death to finally defeat Voldemort.

Later in the book, we will find that, despite the large role Dumbledore had planned for Snape, and the extreme trust he placed in him, Dumbledore never told Snape the entire story. Some pieces, notably the Elder Wand's role and Harry's inability to be killed by Voldemort, he reserved, perhaps feeling them to be too dangerous, or perhaps worrying that knowing the entire plan would cause Snape to become overzealous and unwittingly allow Voldemort's escape.

Questions

 * 1) By the series' conclusion, how has readers' perception about Snape changed? Whose opinion, Harry's or Dumbledore's, was more accurate?
 * 2) Why did Snape counter Quirrell's curse to knock Harry off his broomstick? Could this have been left to Flitwick to protect Harry, or would Dumbledore have known that only Snape knew enough about the Dark Arts to protect him?
 * 3) What are some possible reasons why Snape wanted to get Harry expelled?
 * 4) Why did Snape hesitate before making an Unbreakable Vow to complete Draco's task if he failed?
 * 5) What does Dumbledore mean when he told Harry that after destroying the Gaunt ring Horcrux, "had it not been ... for my own prodigious skill, and for Professor Snape's timely action . . . I might not have lived to tell the tale."
 * 6) What were Dumbledore and Snape arguing about? Why does Snape want to change his mind?
 * 7) Why was Dumbledore so anxious to get to Snape after seeing the Dark Mark when he and Harry reached the Astronomy Tower?
 * 8) Was it more important to Dumbledore about who murdered him or who didn't? Explain.
 * 9) Dumbledore told Harry, "I am a sufficiently accomplished Legilimens myself to know when I am being lied to ...". If Snape had voluntarily opened his mind to Dumbledore, this could have provided sufficient proof that he was truly opposed to Voldemort. Before presenting himself to Voldemort for similar testing, he could have left all thoughts of a change of heart in Dumbledore's Pensieve. Of course he might have left something in some other Pensieve before applying to Dumbledore, instead. In your opinion, given the above, was Dumbledore justified in placing trust in Snape?
 * 10) Was Snape lying to Bellatrix and Narcissa?
 * 11) Given that pureblood family names are known among wizards, surely other Slytherins, including those who became Death Eaters in later life, would know that Snape's blood status is impure. Why is this never brought up? Did Snape denounce his Muggle father?
 * 12) Did Snape's seemingly abusive Muggle father contribute to his joining the Death Eaters, echoing how Voldemort became anti-Muggle?
 * 13) Was Snape's love for Lily romantic in nature or something else?
 * 14) Why was Snape so careless about his personal grooming?

First Five Books
While we do not yet fully understand, it becomes apparent in the first book that Snape absolutely hates Harry in particular, and Gryffindor in general. Just how deeply this hatred runs is only gradually realised; initially, Snape's malice seems rather impersonal, though it is certainly directed at Harry more than anyone else in Gryffindor. Neville Longbottom and Hermione also receive insults and slights from Snape, though never the same degree as Harry. Neville perhaps deserves some disdain, as he often performs poorly in Potions. However, in Harry Potter and the Prisoner of Azkaban, we discover that Neville's worst fear is Professor Snape. That fear, combined with his notoriously poor memory, renders Neville utterly incompetent in Potions, creating horrible messes and melting cauldrons. With a more forgiving and supportive teacher, Neville might have performed much better in class. Harry certainly improves his Potions skill under Professor Slughorn, though he could be considered to have had some additional unsanctioned help.

In Harry Potter and the Prisoner of Azkaban we discover why Snape so dislikes Harry. Harry looks "most extraordinarily like" his father, James Potter. James was involved in a prank that would have left Snape facing a werewolf (Remus Lupin). While James did save Snape's life, Snape never forgave him, claiming James acted only to protect himself from being punished. In Harry Potter and the Goblet of Fire, we also learn that three of the Marauders, James Potter, Sirius Black, and Peter Pettigrew, apparently made a hobby of tormenting Snape, a practice they continued at least until their fifth year at Hogwarts. Harry's appearance always reminded Snape of this dark and painful period in his life, and quite possibly explains some of his maltreatment of Harry, though it in no way excuses it.

Some ambivalence on Snape's part concerning Harry can be seen as early as the first book. Snape was actually protecting Harry, notably during Harry's first Quidditch match. When Harry's broom is Jinxed by Professor Quirrell, Snape attempted to counter it; we have Quirrell's word on that. In Harry Potter and the Order of the Phoenix, Snape agreed to Dumbledore's request to try and teach Harry Occlumency to shield him from Voldemort's mental probes. When Dolores Umbridge requests Veritaserum from Snape, in order to interrogate Harry, from its lack of effect (she apparently had used the entire phial, such that even the slightest sip on Harry's part would have probably constituted the necessary three drops), one must wonder if Snape had provided her with a fake potion. Snape's refusal to provide additional Veritaserum on demand, after Umbridge caught Harry using her fireplace to contact Sirius, could also be construed as defending Harry. And later, it appears Snape believed Harry about Sirius' status, at least enough to investigate his claim and then keep a watchful eye on Harry's whereabouts, and to notify the Order when Harry failed to return from the Forbidden Forest.

Harry Potter and the Half-Blood Prince
Snape plays little direct part in Harry Potter and the Half-Blood Prince despite lending his nickname to the title. Equally, the book is to a large extent all about him. Throughout, he is seen in flash-backs and stories about other characters which illuminate his character, as Harry and company try to discover who the talented Half-Blood Prince really is. Dumbledore explicitly expresses absolute faith in Snape, though he refuses to reveal why; it is this refusal to reveal the reason that has Harry discounting Dumbledore's trust.

Towards the book's beginning, as mentioned above, Snape is finally appointed as the as Defence Against the Dark Arts teacher, a position he had sought for many years. As a result, a new Potions teacher is needed, and Professor Slughorn, a former head of Slytherin house, is coaxed out of retirement. Slughorn accepts students with less than excellent grades for his NEWT-level Potions class, which Snape would never have done. Harry enrolls late and is lent an old textbook, that Harry discovers contains many useful tips hand-written into the margins. As the year progresses, we discover that the textbook is old enough to have belonged to one Eileen Prince, finally identified as Snape's mother, who had married Tobias Snape, a Muggle. We already know (from the Pensieve episode in Harry Potter and the Order of the Phoenix) that Snape was most probably in the same class as Lily Evans (who married James Potter, Harry's father), and from Slughorn's recollections we find that Lily, rather than Snape, was the outstanding natural potions student. The textbook notes are all in the same handwriting and the book is inscribed 'property of the Half Blood Prince'. It also includes descriptions of some spells which Snape admits he created. The implication here is that he recorded all this information into the book; yet if he had been as skilled at Potions as Harry became thanks to the book, it would have been Snape who was remembered as the natural, rather than Lily. All this suggests that in some way the book may have been a collaboration between Snape and Lily. However, given that this is a textbook for 6th year students, and Lily had ended their friendship in their fifth year, Snape was probably the sole contributor. Assuming that they were both in the same NEWT Potions class, however, as everyone in all four houses of Harry's year group seems to be, Snape could have been observing and recording Lily's potion-making from a distance, as a way of trying to stay in touch with her somehow.

The new information adds understanding to the Pensieve scene. In that scene, James was bullying Snape, using a curse on him which we now believe Snape invented. The scene took place during or immediately after Severus Snape's and James Potter's OWLs, which would be their fifth year, before the year in which this textbook would have been used in class. Lily is seen reacting to the injustice, and Snape abusing her out of proportion to what has occurred, as she seems only to have wanted to help him. Together these scenes add credence to the existence of a longstanding relationship between Snape and Lily. She is described as always seeing the good in people others would shun. He is from a doubtful Muggle background, more similar to hers than most of their classmates. Additionally, there is the fact that Snape has not once mentioned Harry's mother, though they apparently were in the same Potions class, almost as if he cannot bear to have her name mentioned. Ordinarily, it would have been so easy to compare Harry against Lily: "Your mother could have whipped that potion up with her eyes closed..." And it is certainly true that he has similarly mentioned Harry's father in that sort of context. All together this has given rise to speculation that Snape was in love with her, even if this was not reciprocated.

Snape is also, in Harry Potter and the Half-Blood Prince, identified as the person who informed Lord Voldemort about the prophecy foretelling his nemesis. This inevitably led to Voldemort seeking out Harry to eliminate him, and in the process killing James and Lily. It makes Snape unwittingly but directly responsible for two people's deaths who were certainly his classmates, one who may have been his rival but the other who may have been (secretly) his one great love. This may explain Dumbledore's unshakable belief that Snape irrevocably rejected Voldemort and the Death Eaters.

Harry Potter and the Deathly Hallows
Snape's loyalty is unclear to us until very late in the final book when it is revealed that he had secretly loved Lily Evans, as speculated above. He had aligned himself with Dumbledore as a means to protect Lily from Voldemort.

This revelation clarifies much of the confusion and mystery that had surrounded Snape. He had hated James Potter for many reasons, including James' ongoing bullying and torment toward him during their school days at Hogwarts, and also James' rescuing Snape from a fatal encounter with the werewolf Lupin, leaving Snape bitterly resenting being forever in James debt. Finally, James spirited away Snape's one love, Lily Evans, daring to have a child with her. To protect Lily from Voldemort, Snape agreed to an open-ended promise with Dumbledore ("Anything!"). Dumbledore, knowing Snape's skill in Occlumency, had Snape spy against Voldemort, and after Lily's death, required him to protect Lily's son, Harry.

This, of course, sets up a major conflict in Snape's life. Every interaction with Harry carries emotional baggage, the more so as Harry, except for his eyes, is the image of his father. Snape cannot help but be reminded of the hated James every time he sees Harry. In Snape's memories, we see him railing about Harry to Dumbledore; interestingly, every trait he attributes to Harry is one that we have seen, to some extent, in James, rather than Harry. Yet, he is sworn to protect Harry, who is the only child of his lost love. In such an untenable situation, is it any surprise that he is bitter? Desperately unhappy himself, he gets what relief he can by making others unhappy also. About the only person Snape does not savage is Dumbledore, who initially exacted the promise from him, and who did do everything he was allowed to do to prevent Lily's death. It is perhaps because of this that Dumbledore dismisses Harry's belief that Snape had been prepared to duel with Sirius; Dumbledore has not experienced directly the depth of Snape's bitterness, and so discounts it. In discussing his reasons for assigning the task of teaching Harry Occlumency to Snape, Dumbledore does admit to having believed that Snape's dislike of Harry could be dealt with.

It is because of this internal conflict, and its final resolution, that the much-despised Snape is one of the most moving, and best-rendered, characters in the entire series. Many readers have been moved to tears by the revelations in chapter 33 of Harry Potter and the Deathly Hallows.

One thing that is not, however, made certain is exactly why Dumbledore kept his belief in Snape's loyalty. At first reading, it seems that he expected Snape to remain loyal because he saw Snape's regret after Lily Evans' death. But strictly speaking, it could have been that Snape's love for Lily had faded over the years, and so he could have turned to Voldemort again. Until the scene with the doe Patronus in Dumbledore's office, which took place in Harry's sixth year, we have no information that Dumbledore could have gotten which unarguably would have proven that Snape was still loyal after fifteen years. What we do know is that once Dumbledore grants someone his trust, he doesn't revoke it lightly. We see evidence that Snape is quite frequently in Dumbledore's company, both in the memories of the Prince and in Harry's direct experience. And while it is never said outright, we believe that Dumbledore has some ability at Legilimency. Dumbledore clearly expected Snape's love for Lily to fade, as shown by his reaction to Snape's Patronus; however, he would not expect Snape's loyalty to fall away, and back towards Voldemort, until Voldemort returned. It is quite possible that Dumbledore had inspected Snape quite thoroughly after the end of Harry Potter and the Goblet of Fire, but we would not see that in the Prince's memories, because that would have been one of the more humiliating experiences in Snape's recent life, and would not have been germane to Harry in any event.

As an interesting sidelight, Severus' motivation is actually implied to some extent by his name. The opera by Donizetti, Poliuto, and the lesser-known opera Polyeucte by Charles Gounod, are both based on the drama Polyeucte martyr by Pierre Corneille. Both operas introduce a romantic subplot in which the Roman general Severus is in love with Polyeuctis' wife Pauline. Though given orders to prosecute Christians, Severus attempts to defend Polyeuctis, who has converted to Christianity, for Pauline's sake. His attempts are unsuccessful, and in the end Pauline dies alongside her husband. The implication is weakened by the number of famous Romans named Severus, including several generals and at least one emperor.

Loyalty
With the exception of Dumbledore, everyone in the books, at one point or another, has their doubts about Snape's loyalty. The doubts of the Death Eaters, as expressed by Bellatrix Lestrange in Harry Potter and the Deathly Hallows, are well-founded: at Karkaroff's hearing, where he is betraying his fellow Death Eaters to the Wizengamot as part of negotiating for a sentence reduction, he claims Snape is a Death Eater, and Dumbledore states that Snape had been working against Voldemort long before Voldemort had fallen. There is no way that this statement, made in what was effectively open court, would have missed being heard by a Death Eater or sympathizer; it is possible, in fact, that Lucius Malfoy was present, and that Harry simply failed to see him in Dumbledore's memory.

This actually is part of the explanation for Karkaroff's conversations with Snape in Harry Potter and the Goblet of Fire. The reader may wonder why Karkaroff is discussing Voldemort's possible return with Snape, who Karkaroff in particular knows had at the very least been in a position to betray Voldemort, and possibly had actually done so. Karkaroff at that point is aware that, having betrayed other Death Eaters in order to save his own skin, he is now equally a traitor in Voldemort's eyes, and believes that if he responds to Voldemort's summons, he will be murdered, if not by Voldemort himself, then by the families or friends of Death Eaters he had betrayed. His trust in Snape is based on his belief that he and Snape are both refugees from the Dark Lord.

Given this understanding, why should Voldemort trust Snape? This also is discussed in detail in Harry Potter and the Half-Blood Prince. In discussions with Bellatrix, Snape tells her and Narcissa Malfoy why Voldemort accepted him back to the Death Eaters organization. Snape implies that Voldemort had examined him by means of Legilimency, which suggests that Snape must be an exceptionally strong Occlumens, not only able to block Legilimency but able to seamlessly generate false images for a Legilimens to perceive. We know, from events in Harry Potter and the Order of the Phoenix, that Voldemort has this ability; he uses it to create perceptions of Sirius Black being tortured in the Ministry of Magic. The fact that Voldemort was unable to perceive Snape doing this leads us to the inescapable conclusion that Snape was significantly stronger at both Legilimency and Occlumency than Voldemort.

Knowing that Snape is loyal to Dumbledore, and knowing the reason for that loyalty, a reader would be well rewarded by studying the portrayal of Snape, and exploring how the many hints of his true loyalty are obscured, and how his loyalty is perceived by other characters. Surprisingly, Snape's influence on the story is almost as great as Dumbledore's, and it is worth study to determine how that influence is hidden from the reader.