The house-elf who first served the Black family at 12 Grimmauld Place was Kreacher.
Kreacher is the ancient, ill-tempered house-elf attached to the Black family home in London. Harry first encounters him when 12 Grimmauld Place becomes the Order of the Phoenix’s headquarters in Harry Potter and the Order of the Phoenix. His behavior reflects his loyalty to the old pure-blood Black family and its prejudices, especially through his devotion to Walburga and Regulus Black.
Kreacher is often confused with Dobby or Winky because all three are prominent house-elves. Dobby originally served the Malfoy family, while Winky served the Crouch family. Kreacher’s story later becomes important when Harry learns about Regulus’s attempt to oppose Voldemort and the role of Slytherin’s locket. After Sirius’s death, Kreacher passes to Harry, who gradually treats him with more understanding.