Mongán mac Fíachnai
Mongán mac Fíachnai (died c. 625) was an Irish prince of the Cruthin, a son of Fíachnae mac Báetáin. Little is certainly known of Mongán's life as only his death is recorded in the Irish annals. He appears as a character in the Cycles of the Kings where he is said to have been the son of Manannán mac Lir and perhaps a reincarnation of the legendary hero Finn mac Cumaill of the Fenian Cycle.
His origin story is told in the Compert Mongáin found in the Yellow Book of Lecan and the Lebor na hUidre.