You are talking about Kreacher, Sirius's house elf, right ... Because Sirius's family belongs to Slytherin, only Sirius has a Gryffindor, so they are very keen on purebred (this is the commonness of Slytherin, as long as they are purebred wizards), so they are very bad to Hermione ... Because Sirius was very bad to Kreacher before his death, Kreacher hated Sirius very much, but because he was a house elf, he had to listen to his master (the highest). Because Kreacher's favorite owner is Sirius's younger brother Ray Guller, Harry gave Kreacher the locket that Ray Guller exchanged for his life, and Kreacher became sincere … I hope I can help you … Please ask questions if you don't understand …