The 'Clan Muircheartaigh Uí Conchobhair (a.k.a. Clan Murtagh O'Connors) were descendants of Irish High-King Toirdelbach Ua Conchobair, via his son, Muircheartach Muimhneach (d.1210). They have been defined by Katherine Simms as:
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... the earliest, most aristocratic and best documented example of increasing nomadism in the northern half of Ireland in the late middle ages. ... In spite of the fact that they were a very numerous branch of the O'Conor family, who supplied five kings to the throne of Connacht, they seem to have vanished away in the early fifteenth century, never to be heard of again.
Clan Muircheartaigh Kings of Connacht
Short history
The family held an overlord position in south Mayo prior to the Norman occupation of Connacht by Richard Mór de Burgh. Their area of control was possibly conterminous with the Diocese of Mayo recognised at the Synod of Kells in 1152. After the Norman take-over in 1235 they attempted with short periods of success to contest for the title of the rump-Kingdom of Connacht in the King's Cantreds with their cousins, the descendants of Cathal Crobhdearg Ua Conchobair. From the 1290s their main base of activity was in West Breifne. After the 1360s their standing was greatly reduced and they returned to County Roscommon as supporters of the O'Conor Roe, gradually fading into obscurity.