Айдан
The 8th century saga "Compert Mongáin", which recounts the deeds of a half legendary son Mongán mac Fiachnai, fathered on Fíachnnae's wife by the sea-god Manannán mac Lir, while Fiachnae campaigned alongside Áedán mac Gabráin of Dál Riata. Mongán was killed in c. 625, in battle against the Britons of the Kingdom of Strathclyde. It may be that Fiachnae was, in fact, High King of Ireland for some time if he is identified with the "Féachno" who followed "Diermait" (presumed to be Diarmait mac Cerbaill) in the "Baile Chuinn Chétchathaig" list.