Cellachán mac Buadacháin (died 954), called Cellachán Caisil, was King of Munster. The son of Buadachán mac Lachtnai, he belonged to the Cashel branch of the Eóganachta kindred, the Eóganacht Chaisil. The last of his cognatic ancestors to have held the kingship of Munster was Colgú mac Faílbe Flaind (d. 678), eight generations earlier. His predecessor as king at Cashel was said to be Lorcan mac Coinlígáin, a distant cousin, the date of whose death is uncertain. The earliest record of Cellachán is an attack on Clonmacnoise in 936. In 939 he was allied with Norse Gaels from Waterford in an attack on the kingdom of Mide. The leader of the Waterford contingent is called mac Acuind (Hákon's son). They took captive the abbots of Clonenagh and Killeleigh but were defeated by the Uí Failge of Leinster. In 941, in a struggle for control of the eastern Déisi, Cellachán came into conflict with the High King of Ireland, Donnchad Donn, and so too with Donnchad's nominated successor Muirchertach mac Néill.
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