Three friends of Job who visited him in his affliction and offered him a way of making sense of his troubles: namely, that he was getting what he deserved. Job's friends maintained that misfortunes were sent by God as punishments for sin, and thus despite Job's apparent goodness, he must really be a terrible sinner. Job persistently disputed them, saying that God is supreme and mysterious — that God can send misfortunes to both good and wicked people and may not be second-guessed.
Note: A “Job's comforter” is someone who apparently offers consolation to another person but actually makes the other person feel worse.