Half-Blood Prince (book only),
Deathly Hallows (movie only)
Kreacher was an aged House-elf who served the House of Black and was fond of her mistress Walburga Black. He is pretty much unpleasant to Sirius Black and Harry Potter. He also hated Hermione Granger and the Weasleys because of their kind of Muggle-borns and Blood traitors. He fought at the Battle of Hogwarts and continued serving Harry Potter for the rest of his life.