From the book "The Oxford History of Ireland" edited by R. F. Foster, 1992, ISBN 0-19-285271-X, page 37:
The Eóganacht of Munster were pushed aside in the 10th century by the Dál Cais of North Munster. They straddled the strategic waterway of the Shannon. On his death notice in 951 Cennétig, king of Dál Cais, is called 'king of North Munster'; his son Brian Bóruma, or Brian Boru (ancestor of the O'Briens), who succeeded in 976, was to make himself king of Ireland and rival of the Uí Néill.