Historical king of Dál nAraide (d. c. 625 CE per the Irish annals); medieval-literary demigod son of Manannán mac Lir by Caintigern, queen of Dál nAraide and wife of King Fíachna mac Báetáin. The Compert Mongáin (8th c. CE, surviving in three variants) preserves the bargain-night conception in which Manannán saved Fíachna's life in Scottish campaign in exchange for a night with Caintigern. Taken to the Otherworld at age three days; raised by Manannán in Tír Tairngire until age twelve or sixteen; returned to rule from Ráth Mór in Mag Líne. Parallel tradition makes him a reincarnation of Finn mac Cumhaill of the Fenian Cycle (Scél asa mberar co mbad hé Find mac Cumaill Mongán). Killed on Islay c. 625 by a stone hurled by a Briton named Artúr mac Bicoir — a death he had foretold as a child walking the beach with his mother. Mongán is the registry's clearest historical-figure-with-medieval-divine-paternity-tradition case: an actually-historical 7th-century king whose contemporary Annals record his death normally, but whose 8th-century-and-after literary tradition elaborates a divine paternity through a major Tuatha Dé deity.