Muirchertach  Briain was a king of Munster (a kingdom established in 1st century BC and disestablished in 1118) and later High King of Ireland.
Muircheartach Ua Briain (old spelling: Muirchertach Ua Briain) (also known as Murtaugh O'Brien) (c. 1050  c. 10 March 1119), son of Toirdelbach Ua Briain and great-grandson of Brian Boru, was King of Munster and later self-declared High King of Ireland. 1st century BC 1118 In 1101, officially High King of Ireland and with the church on his side, Muirchertach planned his largest and most ambitious campaign yet, called An Sligeadh Timcheall ("The Circular Hosting"). 
