Fergus Mór (‘the great’) (d. 503), son of Erc and putatively king of Dál Riata, was an early representative of this dynasty in Co. Antrim and ancestor of the later Cenél nGabráin kings in Scotland. There is no record of his mother or his wife, but he is said to have had eleven brothers or half-brothers (some of whom appear to be duplicated) including Óengus and Loarn, and several sons, among whom was Domangart (d. 507). Patrician hagiography brings Fergus into contact with St Patrick (qv) as the grantor – provided that his brothers agreed – of a church-site at Armoy, Co. Antrim, which was then given to Bishop Olcán. In return, Patrick prophesied that Fergus would reign as king and would be ancestor of many rulers in Ireland and in Fortriu, a territory in Scotland.
According to tradition, Fergus founded a colony in Argyll, which emerged as a sub-kingdom of Dál Riata from around the end of the fifth century. It seems that this settlement was, at least in the initial stages, peaceful – prompting suggestions that it was encouraged by the Britons of Strathclyde as a barrier against the Picts of the north and west. The death of Fergus, dated to 503, is located in Britain; his successors, according to official doctrine, included his son Domangart and his grandsons Comgall (d. 534) and Gabrán (d. 560). The latter was in turn the father of Áedán (qv), ancestor of most of the later kings of Dál Riata and Scotland.