Muircheartach Ó Briain (Murtogh O'Brien)

Muircheartach Ó Briain (died 1343), anglicised Murtogh O'Brien, was a younger son of Toirdhealbhach Mór Ó Briain. He became King of Thomond in 1317 after his cousin Donnchad lost Richard de Clare's support and fled to Connacht.

When Richard de Clare invaded with Norman troops, Muircheartach joined his ally Conor O'Dea and routed them at Dysert O'Dea in 1318, where de Clare was killed, ending Norman power in Thomond. He ruled until his death in 1343.