Children: Gregory Goyle
Kreacher was 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 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. He is described to have many folds of skin as well as white hairs in his ears, and he is supposed to have a deep "bullfrog" voice.
Under Master Harry Potter
- Dumbledore: "Give him an order. 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."
- Kreacher: "Won't, won't, won't, WON'T!"
- Harry: "Kreacher, shut up!"
- — Harry Potter, Albus Dumbledore and Kreacher in the Dursley Family's house[src]
Sirius left all his belongings, including Kreacher, to his godson. Harry, who had no desire to have anything to do with Kreacher, ordered him to work in the kitchens at Hogwarts with the other house-elves at Dumbledore's suggestion, where he and the other house-elves could keep a close watch on him. This eventually turned out to Harry's advantage, as Kreacher — along with Dobby, another house-elf working at Hogwarts — 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.
- Harry: "Have you ever seen this before? Kreacher?"
- Kreacher: "It's Master Regulus's locket."
- Harry: "But there were two, weren't there? Where's the other one?"
- Kreacher: "It was here, in this house."
- Harry: "Where is it now? Did someone take it?"
- Kreacher: "He came in the night. He took many things, including the locket."
- Harry: "Who did? Who was it, Kreacher?"
- Kreacher: "Mundungus...Mundungus Fletcher!"
- — Harry asking Kreacher about the whereabouts of Salazar Slytherin's Locket.
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 for tracking down Mundungus. Kreacher's joy at being given a Black family "heirloom" as his own caused him to drastically change his view of Harry. He even started to treat Hermione, 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.
The morning of Harry, Ron, and Hermione's attempt to break into the Ministry of Magic to find the real locket of Salazar Slytherin, Kreacher served them a breakfast of rolls and coffee and promised a meal of steak-and-kidney pie to be waiting for them when they returned, but after successfully obtaining the real locket of and escaping the Ministry, Harry, Ron, and Hermione were no longer able to go back to Grimmauld Place because they left Yaxley inside the Fidelius Charm. Harry and Hermione concluded that it would be too risky to summon Kreacher since Grimmauld Place was most likely taken over by Death Eaters.
- "Fight, fight for my master, the defender of the house-elves! Fight the Dark Lord, in the name of brave Regulus! Fight!"
- —Kreacher leading the house-elves during the Battle of Hogwarts.[src]
Kreacher led the house-elves of Hogwarts in battle against the Death Eaters during the attack on Hogwarts, for Harry Potter, defender of the house-elves, and for the sake of the memory of his long-dead master Regulus, bringing to mind that, although he was a Death Eater, he had died fighting Lord Voldemort.
It is not specified whether he survived the Battle of Hogwarts, but Harry, who wanted to go to bed after the battle, wondered if Kreacher could bring him a sandwich, implying that he did in fact survive. He didin't continued to work in the Hogwarts kitchens and entered the service of the Potter family.
Serving the Potter Family
After graduating from Hogwarts and moving to 12 Grimmauld Place, Harry Potter called Kreacher to return to work at the former home of their former masters. Kreacher left the kitchens of Hogwarts and devoted himself exclusively to the Potter family. At Christmas 2017, Kreacher was in charge of taking gifts from Albus, James, and Rose to Gryffindor Tower and prevent them from trying to open them early. Kreacher also advised the family to contact them through the Floo Network.
- "Oh, my poor mistress, what would she say if she saw Kreacher serving him?"
- —Kreacher complaining about his master[src]
Kreacher was extremely devoted to all members of the Black family except Sirius Black, whom he hated. Sirius claimed that he was slightly less devoted to Sirius' father than he was to his mother but also said he caught him snogging a pair of his fathers old trousers. Kreacher was often seen taking orders from a portrait of Sirius' mother. Considering Kreacher was disloyal to people who treated him in a horrible manner, the Black family must have treated him with kindness.
Out of all members of the Black family, Kreacher's bond with Regulus appeared to be the strongest. In fact it was partially because of Kreacher that Regulus turned against Voldemort; after discovering the cruel way his master treated Kreacher, and realising that his immortality came from creating Horcruxes, Regulus and Kreacher went to the cave to steal Voldemort's locket. Regulus sacrificed himself to retrieve the locket, even though he could have ordered Kreacher to drink the Drink of Despair for him, showing that he truly did care about Kreacher. The elderly house elf was still devastated by Regulus' death, eighteen years after it happened. He felt he had failed Regulus by being unable to destroy Voldemort's locket.
Unlike Regulus, Sirius was horrible to Kreacher, treating him as though he was not worth anything, but also ordering him about. Sirius' behaviour originated from his hatred of his family and the house of Black itself. However Albus Dumbledore said that he was usually kind to house elves. Kreacher hated Sirius, because of his cruel attitude towards him, and he betrayed Sirius to Bellatrix Lestrange and Narcissa Malfoy which resulted in Sirius' death. Had Sirius treated Kreacher kindly his death might have been avoided.
At first Harry and Kreacher had an antagonistic relationship. When Harry attempted to discover if Lord Voldemort had captured Sirius, Kreacher lied to him and claimed he was alone in Sirius' house. After Sirius' death, Harry placed part of the blame on Kreacher and part on Severus Snape, but put most of the blame on himself. Under Harry's ownership, Kreacher was ordered to work in the Hogwarts kitchens. Harry then ordered him and Dobby to spy on Draco Malfoy and made sure there were no loopholes in the instructions he'd given Kreacher. When Kreacher and Dobby returned from spying on Malfoy, Harry congratulated Dobby but ignored Kreacher.
However whilst living in the house of Black, Harry learned a bit about Kreacher's past and began to feel more sympathetic towards him. He tried to be kind to Kreacher and gradually their relationship improved. Harry then gave Kreacher the fake Slytherin's Locket with the note from Regulus, saying Regulus would have wanted him to have it, as Kreacher adored having a Black family heirloom for himself. Kreacher eventually grew quite friendly towards Harry and company, especially after Harry gifted him the locket, and started cooking for them, cleaning the house, and reminding him to wash his hands before dinner, during their hideout there in 1997. Harry also congratulated him when he succeeded in capturing Mundungus Fletcher. During the Battle of Hogwarts, Kreacher led the house elves against Lord Voldemort and his followers, telling them to fight for Harry and the deceased Regulus.
Kreacher had a bad relationship with Dobby mainly because they had, at first, opposite opinions of Harry Potter. The two house elves even got into a brawl at one point after Kreacher insulted Harry. However they did work together to spy on Draco Malfoy.
After leaving the kitchens of Hogwarts, Kreacher begins to serve the Potter family and help in whatever it takes to master your Harry Potter, his wife and children. Kreacher also leaves to tease Hermione, but still feel some bitterness about having to call her master.