A son of Conchobar mac Nessa, king of Emain Macha, who goes into voluntary exile to protest the treacherous killing of the sons of Uisnech, whose surety in passage he had been. In the epic Táin Bó Cuailnge [Cattle Raid of Cooley], he travels with the invading army of Connacht under Queen Medb [Maeve]. Later he prevents Fergus mac Róich from killing Conchobar. Later still, Conchobar on his deathbed sends for Cormac to replace him in the kingship. As Cormac starts this journey of reconciliation he is murdered by a band of Connachtmen returning from a raid in Ulster. He is sometimes thought to have married Niam (2), daughter of Celtchair, after her treacherous marriage to Conganchnes. According to genealogical tracts, he later takes Étaín (1) as a wife, presumably after the death of her usual mortal husband, Eochaid Airem. Also a character in Togail Bruidne Da Derga [The Destruction of Da Derga's Hostel]. He may be identical with Cormac (1), husband of Étaín Óg.