The O'Briens, one of the few native Irish families with a peerage, descend in the male line from Brian Boroimhe, Prince of Thomond (North Munster or the north part of southwest Ireland, roughly commensurate with an area centered on modern Co. Clare) and Chief of the Dalgais, who became High King of Ireland 1002 and was killed at the victory over the Danes of Clontarf 23 April 1014. [Burke's' Peerage, p. 1495]