The house elf who helps Harry Potter is Dobby.
Dobby is introduced in Harry Potter and the Chamber of Secrets as a house elf serving the Malfoy family. Although he initially causes trouble for Harry, his actions are intended to keep Harry away from Hogwarts because he knows the Chamber of Secrets is about to be reopened. His warnings show that he is courageous despite being bound to obey his owners.
Harry eventually frees Dobby by tricking Lucius Malfoy into giving him a sock. Once liberated, Dobby chooses his own work and later serves at Hogwarts, where he helps Harry and his friends on several occasions. He also rescues the prisoners from Malfoy Manor in Harry Potter and the Deathly Hallows.
Hokey, Winky, and Kreacher are also house elves, which makes them plausible distractors, but none is the elf most closely associated with helping Harry. Dobby dies while rescuing his friends, and Harry later gives him a proper burial.