Ahithophel
Ahithophel was a wise counselor to David who defected to Absalom's side during Absalom's rebellion, but later committed suicide when his advice was not followed.
Ahithophel the Gilonite was David's most trusted counselor—'as if one consulted the oracle of God' (2 Samuel 16:23)—until he defected to Absalom's rebellion, becoming its chief strategist. His counsel to Absalom to take David's concubines publicly and to pursue David immediately with a swift strike was sound military advice; had Absalom followed the second recommendation, David would have been destroyed (2 Samuel 16–17). When Absalom instead accepted Hushai's counsel—by divine design—Ahithophel recognized that the rebellion was doomed and hanged himself, becoming the only person in the Old Testament explicitly said to have died by suicide (2 Samuel 17:23). Many scholars see his story as a precursor to the betrayal and death of Judas Iscariot.