Brien, Bryan, O' Brien, O’ Brian, Ó Briain
Ó Briain comes from the personal name Brian, and denotes a descendant of Brian Boru, King of Ireland in the 11th Century. Brian Boru was a member of the Uí Toirdealbhaigh sept, who were part of the Dál gCais tribal grouping, and were based in the Clare / Limerick area. The O’ Briens subsequently spread to counties Tipperary and Waterford. Today the name is the sixth most numerous in Ireland, and is strongest in the province of Munster, in particular county Limerick where it is the most numerous surname.