Dalriada defined as straddling Irish Channel from Antrim (in Ireland) to Argyll. He appears under the heading "Gaels of Argyll." King of Scots of Dalriada ca. 490. (Williamson, David. Debrett's kings and queens of Britain. Topsfield, Mass. : Salem House Publishers, 1986, pg. 228).
The first Dalriad king in Scotland. Came from Ulster with his brothers, Lorn and Angus, and took possession of Cantyre and adjacent isands (The concise dictionary of national biography. Part 1 : from the beginnings till 1900. London : Oxford University Press, 1969, pg. 426).
www site Directory of royal genealogical data seems to confuse he and his father.
The historical record, such as it is, consists of an entry in the Annals of Tigernach, for the year 501, which states: Feargus Mor mac Earca cum gente Dal Riada partem Britaniae tenuit, et ibi mortuus est. (Fergus Mór mac Eirc, with the people of Dál Riata, held part of Britain, and he died there.) However, the forms of Fergus, Erc and Dál Riata are later ones, written down long after the 6th century. The record in the Annals has given rise to theories of invasions of Argyll from Ireland, but these are not considered authentic.
Fergus is also found in the king lists of Dál Riata, and later of Scotland, of which the Senchus Fer n-Alban and the Duan Albanach can be taken as examples. The Senchus states that Fergus Mór was also known as Mac Nisse Mór. These sources probably date from the 10th and 11th centuries respectively, between 30 and 40 generations after Fergus may have lived.
The Senchus and the Duan name Fergus's father as Erc son of Eochaid Muinremuir. A Middle Irish genealogy of the kings of Alba gives an extensive genealogy for Fergus: [Fergus] m. h-Eircc m. Echdach Muinremuir m. Óengusa Fir m. Feideilmid m. Óengusa m. Feideilmid m. Cormaicc, and a further forty-six generations here omitted. While it was suggested some believe Fergus claimed lineage to Arthur, the historian John Morris has suggested, instead, that Fergus was allowed to settle in Scotland as a federate of Arthur, as a bulwark against the Picts.
These sources, while they offer evidence for the importance of Fergus Mór in Medieval times, are not evidence for his historical career. Indeed, only one king in the 6th century in Scotland is known from contemporary evidence, Ceretic of Alt Clut, and even this identification rests upon a later gloss to Saint Patrick's Letter to Coroticus. The first kings of Dál Riata whose existences are reasonably sure are Fergus's grandsons Gabrán mac Domangairt and Comgall, or perhaps his great-grandson Áedán mac Gabráin (wikipedia)