Cú Ceanain mac Tadhg, Prince of Uí Díarmata, ancestor of the Concannon family, died 991 Cú Ceanain mac Tadhg was a member of the Síl Muiredaig dynasty, who ruled as kings of The Connachta in what is now central County Roscommon.
Here a branch of the kindred seized territory and renamed it Uí Díarmata, after its founder, Diarmada Finn mac Tomaltaig, who was in turn a great-grandson of King Indrechtach mac Muiredaig (died 723).
[citation needed] Cú Ceanain was a son of a previous king, Tadhg mac Muircheartach (died 971) but had not succeeded himself.
A war between himself and the then king, Gillacommain mac Niall, brought about both their deaths in 991.
All subsequent kings of Uí Díarmata descended from him, while Cú Ceanain's grandson, Muirgeas ua Cú Ceanainn, was the first to adopt the style that subsequently became the dynasty's surname, Concannon.