Cormac mac Cuilennáin was a 9th-century Irish bishop and the king of Munster who ruled from 902 until his death in 908. A member of the Eóganachta clan, he held both significant religious and political authority during a period of shifting power in Ireland. He is remembered as a scholarly figure and a saintly ruler who sought to expand his influence through military campaigns. His life ended during the Battle of Bellaghmoon, where he was killed in Leinster following a military engagement against the Leinstermen.