Kreacher

Kreacher is a house-elf who serves Harry Potter. For most of his life, Kreacher served various members of the House of Black, including Sirius Black and his mother (whom Kreacher remembers fondly and still calls "his mistress").

Kreacher is considered somewhat of a liability by the Order of the Phoenix, who use the Blacks' house, number twelve, Grimmauld Place, as headquarters, because as a house-elf, Kreacher overhears things of a sensitive nature. He is forbidden to speak of the most important things, but in Harry Potter and the Order of the Phoenix, Sirius accidentally tells him to leave and he tells Narcissa Malfoy (who is the only Black family member left that Kreacher respects) several small things that were not considered to be of any importance, yet led to Sirius' demise.

When Sirius died, he willed all his belongings (including Kreacher) to Harry. Harry, who had no desire to have anything to do with Kreacher, told him to work at Hogwarts with the other house-elves, where they could keep a close watch on him. Kreacher &mdash; along with Dobby, another house-elf working at Hogwarts &mdash; tailed Draco Malfoy for Harry to try to find out what he was up to in Half-Blood Prince.