Muggles' Guide to Harry Potter/Characters/Elladora Black

Overview
Elladora Black was a pure-blood witch and an aunt to Sirius and Regulus Black. Apparently she started the tradition of cutting off the heads of house elves when they got to a certain age.

Order of the Phoenix
While looking at the Black Family tapestry, she is one of the names Sirius points out to Harry and tells him that it was her who began the tradition of cutting off the heads of the family house-elves and stuffing them when they got too old to carry tea trays.

Relationships with Other Characters
Judging by the way Sirius sarcastically refers to her as "Dear aunt Elladora" it seems that she did not get along with her nephew. At the very least he held her with as much contempt as he did the rest of his family.

Greater Picture
Much like the Malfoys, she is a great example of how poorly many wizards, apparently especially pure-blood wizards, treat their house-elves, going so far as to outright murder them when they get too old.