Kreacher

"Kreacher is what he has been made by wizards, Harry. Yes, he is to be pitied. His existence has been as miserable as your friend Dobby's. He was forced to do Sirius's bidding, because Sirius was the last of the family to which he was enslaved, but he felt no true loyalty to him. And whatever Kreacher's faults, it must be admitted that Sirius did nothing to make Kreacher's lot easier."

- Albus Dumbledore on Kreacher

Kreacher is an aged house-elf who served the House of Black with fanatical loyalty for most of his life, until he was left to Harry Potter upon the death of Sirius Black in 1996. He was particularly fond of "his mistress" Walburga Black, who died in 1985, but whose portrait still shrieks orders from the wall in the front hall of the Black house. After Mrs. Black's death, Kreacher let the home fall into disarray, doing little, if any, cleaning. He was also fiercely loyal to Regulus Black, for whom he fought in the Battle of Hogwarts along with many other house-elves.

Under Regulus Black
In 1979, when Lord Voldemort told Regulus Black that he needed an house-elf, Regulus volunteered Kreacher, saying it would be a honour to serve the Dark Lord. Voldemort took Kreacher to the Horcrux Cave and forced him to drink the potion in the basin so that Voldemort could place Salazar Slytherin's Locket in the basin. Voldemort then left, leaving Kreacher to drink from the lake and die at the hands of the Inferi. However, Voldemort did not remember (or did not realize) that house-elves have their own special type of magic and Kreacher was able to Disapparate from the cave when Regulus told him to come home.

Regulus later had Kreacher take him back to the Horcrux Cave. Regulus drank the potion himself and ordered Kreacher to switch Slytherin's Locket with a fake locket and then go home and destroy the "real" locket, leaving Regulus to die in the cave. He also ordered to never tell his family what had happened to Regulus. Kreacher left as ordered but was unable to destroy the locket, despite his many attempts.

Under the Order
"I warned Sirius when we adopted twelve Grimmauld Place as our headquarters that Kreacher must be treated with kindness and respect. I also told him that Kreacher could be dangerous to us. I do not think that Sirius took me very seriously, or that he ever saw Kreacher as a being with feelings as acute as a human's."

- Albus Dumbledore after Sirius's death

Kreacher was loyal only to pure-blood wizards in general, Walburga Black in particular. After her death, however, Sirius Black became Kreacher's master, despite having been considered a blood traitor. Kreacher was hostile to Sirius and to the entire Order of the Phoenix when they used 12 Grimmauld Place as their Headquarters, but was forced to serve Sirius. He was still known to steal Black family heirlooms during the Order's cleaning efforts and hide them in his den in the kitchen cupboard. In turn, Sirius treated Kreacher cruelly.

Kreacher was considered somewhat of a liability by the Order of the Phoenix, who used the Blacks' house as headquarters; as a house-elf, Kreacher overheard things of a sensitive nature. He was forbidden, however, to speak of the most important things, but sometime in December 1995, Sirius accidentally told him to leave. Taking that to literally mean leave the house, he went to the Malfoys, close relatives of the Blacks, and told Narcissa Malfoy née Black and Bellatrix Lestrange née Black several details that were not considered to be of any importance, yet led to Sirius' demise. Narcissa and Bellatrix treated Kreacher kindly to get him to cooperate with them; thus, when Harry Potter Flooed Grimmauld Place in June asking if Sirius was there, Kreacher lied. This convinced Harry that his vision of Sirius being tortured in the Department of Mysteries was true, and led him and his friends to attempt to rescue him. This resulted in a battle in which Sirius was killed by Bellatrix.

Under Harry Potter
""Give him an order," said Dumbledore. "If he has passed into your ownership, he will have to obey. If not, then we shall have to think of some other means of keeping him from his rightful mistress." "Won't, won't, won't, WON'T!" Kreacher's voice had risen to a scream. Harry could think of nothing else to say, except, "Kreacher, shut up!""

Sirius' will left all his belongings, including Kreacher, to his godson. Harry, who had no desire to have anything to do with Kreacher, and to keep him out of the Order's way, ordered him to work at Hogwarts with the other house-elves, where he could keep a close watch on him. This eventually turned out to Harry's advantage, as Kreacher &mdash; along with Dobby, another house-elf working at Hogwarts &mdash; tailed Draco Malfoy for him when he suspected Malfoy to be up to no good. Kreacher disliked Harry, and only followed his orders because he had to. For Christmas in 1996, Kreacher gave Harry a box of maggots.

In 1997, Harry made Kreacher tell him about Regulus Arcturus Black, who he had correctly deduced was the R.A.B. who took Salazar Slytherin's Locket from the Horcrux Cave. Kreacher told Harry, Ron, and Hermione the story of the two lockets and his inability to destroy the real one. He told Harry that Mundungus Fletcher stole the real locket and Harry rewarded him with Regulus's fake locket. Kreacher's joy at being given a Black family "heirloom" as his own drastically changed his opinion of Harry, whom he started to serve properly. He even started to treat Herminone, whom he had previously disdained as a "Mudblood", a bit better. Hermione turned out to be right about Kreacher; he was nice to those who treat him well.

"Fight, Fight for my master, the defender of the House elves. Fight for brave Regulus!"

- Kreacher leading the house-elves during the Battle of Hogwarts

Kreacher lead the house-elves of Hogwarts in battle against the Death Eaters during the attack on Hogwarts, for the sake of the memory of his long-dead master Regulus, reminded that, although he was a Death Eater, he ended fighting Lord Voldemort.

It is not known whether he survived the battle but Harry who wanted to go to bed after the Battle of Hogwarts wondered if Kreacher could bring him a sandwich, implying that he did indeed survive the battle.

Etymology
Kreacher's name is most likely derived from the word "creature." Reminiscent of the German "kriecher" derived from "kriechen," meaning "to creep, crawl, cringe, grovel, tuckle, or fawn upon."

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows

Notes and references
Кикимер