Brian Boru

Brian Boru was an Irish king who ended the domination of the High Kingship of Ireland by the Uí Néill and probably ended Viking invasion/domination of Ireland. Brian built on the achievements of his father, Cennétig mac Lorcain, and especially his elder brother, Mathgamain, Brian first made himself king of Munster, then subjugated Leinster, eventually becoming High King of Ireland. He was the founder of the O'Brien dynasty, and is widely regarded as one of the most successful and unifying monarchs in medieval Ireland.