Muggles' Guide to Harry Potter/Characters/Fluffy

Overview
Fluffy is an extremely large three-headed dog, apparently loyal to Hagrid. He is apparently modeled on Cerberus, the three-headed dog who guards the entrance to the Underworld in Greek mythology.

Philosopher's Stone
At the Arrival Feast, Professor Dumbledore announces that the third-floor corridor "is off-limits to any who do not wish to suffer a painful death." A couple of weeks later, Harry, Ron, Hermione, and Neville stumble into this hallway while trying to avoid Filch. It appears the threat is a large and fierce three-headed dog. They escape unharmed, but Hermione notices that the dog is apparently guarding a trap door.

Professor Quirrell bursts into the Hallowe'en Feast to report a troll in the dungeons. Harry and Ron recall that Hermione has run off to a washroom to cry, and break away from the students being chaperoned back to Gryffindor Tower to let her know; as they head back to the washroom they see Professor Snape apparently headed for the third-floor corridor. A few days later, Harry sees Filch bandaging Snape's leg, and overhears Snape saying something about watching what the other two heads are doing, and concludes that Snape has been trying to get past the dog.

Just before Christmas, the Trio ask Hagrid about what the dog would be guarding. Hagrid mentions that the dog's name is Fluffy, to general consternation.

Shortly after exams are ended, the Trio ask Hagrid about the circumstances surrounding the dragon's egg that he acquired, and Hagrid mentions that the person who had traded him the egg had been most interested in Hagrid's skill with exotic animals, notably Fluffy. Hagrid mentions that he had told that person how Fluffy is very fond of music, that he goes right to sleep if you play him a tune, and Harry immediately guesses that the person was Snape, and that was the only piece of information he needed to reach the Stone, the artifact that the Trio believe Fluffy is guarding.

That night, the Trio resolve to brave the trap door, and what lies beyond it, in order to help protect the Stone from whoever is trying to steal it, who they suppose to be Snape. The first stage of this expedition is Fluffy, and Harry puts him to sleep by playing a tune on a whistle that Hagrid had gotten him for Christmas.

When Harry is recovering in the Hospital Wing, Hagrid visits, and is full of remorse that he had been the one who told the person who gave him the dragon's egg how to get past Fluffy, that being the one piece of information he needed. Harry is stern with him, reminding him that the driving force in the matter was Voldemort, and that Voldemort would have found the information somewhere even if Hagrid hadn't given it to him.

Chamber of Secrets
Hagrid mentions that Fluffy has been released into the Forbidden Forest.

Strengths
Like any dog, Fluffy has speed and teeth on his side in any physical confrontation; additionally, because the three heads can presumably communicate with each other, one supposes that any attack would be coordinated to come from three directions at once. Fluffy is also loyal to Hagrid, and apparently a fierce guard dog.

Weaknesses
It would appear that Fluffy can be put to sleep by music.

Relationships with Other Characters
We only see Fluffy guarding the trap door against the Trio and Neville, and gather that he is quite fierce in that defence. We presume, from Hagrid's tone when speaking of him, that Fluffy sees Hagrid as his master, but we do not see them interacting.

Analysis
We note that Fluffy is put to sleep by music, even the sort of aimless tootling that Harry is able to provide on the carved whistle he has received from Hagrid. This would tie in with the Greek myth of Orpheus, who got past Cerberus by means of his music.

Fluffy, Norbert, Aragog, and Buckbeak, are four of Hagrid's pets that are specifically mentioned by name. All of them are large and dangerous, and serve to highlight Hagrid's lack of fear of creatures that most wizards would class as dangerous. This light-heartedness in the face of dangerous creatures will be a recurring theme with Hagrid.