He was the son of Forggus mac Cellaig (died 756), a previous king.
[1] The sept of Uí Briúin he belonged to was the Síl Cellaig of Loch Cime (Lough Hackett, near Headford in modern County Galway) named for his grandfather Cellach mac Rogallaig (died 705).
[2] However, the Annals of Ulster say that Muirgius mac Tommaltaig (died 815) became king after defeating Cináed mac Artgail (died 792) at the Battle of Sruth Cluana Argai (Cloonargid, Roscommon, Co.) in 792.
[3] His death is recorded in this annal as King of Uí Briúin.
This biography of a member of an Irish royal house is a stub.