https://en.wikipedia.org/wiki/Domnall_Midi

Domhnall Mac Murchada , called Domnall Midi , was High King of Ireland. He belonged to the Clann Cholmáin branch of the Uí Néill. Clann Cholmáin's pre-eminence among the southern Uí Néill, which would last until the rise of Brian Bóruma and the end of the Uí Néill dominance in Ireland, dates from his lifetime.

Domnall was chief of Clann Cholmáin for almost fifty years, and High King of Ireland for twenty. In spite of this, and his importance as a dynast, the Irish annals contain relatively few reports of his activities. He was a patron of the Columban churches, particularly Durrow Abbey, where he is buried.