He ruled for a year, before he was defeated by Cormac, with the assistance of Tadg mac Céin and Lugaid Láma, in the Battle of Crinna.
The Lebor Gabála Érenn makes no reference to Fergus' descent.
[2] The Annals of the Four Masters name Fergus' father as Imchad, but traces his descent no further.
[3] The Lebor Gabála synchronises Lugaid's reign with that of the Roman emperor Commodus (180–192).
The chronology of Keating's Foras Feasa ar Éirinn dates his reign to 203–204, that of the Annals of the Four Masters to 225–226.