[Ir., son of hazel].
A king/warrior of the Tuatha Dé Danann, best remembered as the first of the three brothers who kill the hero Lug Lámfhota, along with Mac Cécht (1) and Mac Gréine, in revenge for Lug's having killed their father, Cermait. Often described as the husband of Banba, an incarnation of Ireland. In Christian Irish tradition Mac Cuill is portrayed as a champion of paganism against St Patrick. Muirchú's Life of Patrick (7th cent.) describes the saint, with superior magical power, converting Mac Cuill to Christianity and setting him adrift, as a penance, in a rudderless, oarless coracle which bears him to the Isle of Man, where he becomes a missionary. From the episode evolved the persona of St Maughold of Manx tradition.