Kreacher was an old house-elf who served the Black family for his whole life, until Sirius Black transferred everything he owned, including Kreacher, to Harry Potter. He was fond of "his mistress," Walburga Black, and preserved her portrait for years.
During this time, Kreacher was hostile to the entire Order of the Phoenix, especially Sirius Black, who was considered a blood traitor. He specifically hated Muggle-borns, or "Mudbloods," such as Hermione Granger. Sirius often ordered Kreacher to go up to the attic, so the Order could enjoy a few hours of peace.
Kreacher appeared to be more friendly in 1997, most likely because he got over the fact that his "mistress" died. He listened to Harry, and was respected more.
Kreacher and Regulus could almost be considered friends, or even brothers. Regulus was loyal to Kreacher, and Kreacher was loyal to him. Together they found Slytherin's locket, and replaced it with a fake. Regulus's death may be another reason for Kreacher's grumpiness.
Originally, Kreacher and Harry seemed to hate each other. But when he became Harry's house-elf, they respected each other more. Harry began to respect Kreacher and complimented him on his work. Kreacher stopped spying on Harry, and deeply respected him.
Kreacher never liked Hermione, because of the fact that she was a Muggle-born. Harry later instructed Kreacher to respect Hermione, and Kreacher left her alone.
- Harry Potter and the Order of the Phoenix (book) (First appearance)
- 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 (book)
- Harry Potter and the Deathly Hallows (book)
- Harry Potter and the Deathly Hallows: Part 1 (film)
- Harry Potter and the Deathly Hallows: Part 1 (video game)
- LEGO Harry Potter: Years 5-7