Cormac Mac Carthaig

Cormac Mac Carthaig (died 1138) was King of Munster.

Since the 10th-century the kingship of Munster had been held by the Dál gCais at the expense of the original dynasty, the Eóganachta. In 1983, Henry Alan Jefferies stated:

Since the days of Ceallachán († 954), their fortunes had gone into grave and seemingly endless decline. Not only did they lose the kingship of Munster to Brian Boru, but by the 1070s Brian's descendants had wrested possession of Cashel itself from them. The dispossessed remnant of the Eóghanacht of Cashel migrated westwards and by the reign of Muiredach son of Cárthach, they may have occupied some location in the Emly-Duhallow district. Certainly the early expansion of the Mac Carthys suggests a north-west Cork provenance. Muiredach's death in 1092 was swiftly followed by the murder of his brother and successor at the hands of Ceallachán O'Callaghan. In view of this killing, and his designation as 'O'Callaghan of Cashel' at a time when that district had long been lost to the Eóghanacht, I would suggest that Ceallachán usurped the kingship of the Eóghanacht of Cashel and retained it until his death. It is my contention that his death in 1115 was a Mac Carthy action which opened the way for the rise to power of Tadhg son of Muiredach Mac Carthy.

Not until the early 12th century did members of a sept of the dynasty, the Mac Carthaigh clan, be led by the brothers Tadg Mac Carthaig (king of Desmond 1118-1123) and Cormac Mac Carthaigh, sons of Muireadach mac Carthaig (died 1092).

Muirchertach Ua Briain (c. 1050–c. 1119) was both King of Munster and High King of Ireland. He was of the Dál gCais dynasty, and a great-great grandson of Brian Boru (c. 937-1014).

...
Wikipedia