Son of Cian (3), grandson of Ailill Aulomm, who has the vision of Clídna as the noblest and most beautiful of women, attended by three brightly coloured birds. In adventures in the Otherworld he comes to a mysterious island ruled by two sons of Bodb, where a woman tells him that all the kings of Ireland from Conn Cétchathach [of the Hundred Battles] live here. He also meets Connla (2) and his fairy woman as well as the apple tree that lured him. Returning to the mortal world, Tadg realizes he has been gone a year. An earthly alliance with Cormac mac Airt proves disappointing. In a campaign against Ulster, Cormac promises allies as much land as they can circle in a chariot. When Cormac learns that Tadg has his sights on Tara, he bribes Tadg's charioteer not to complete the circle, thus depriving him of the award. Learning of this, Tadg kills the charioteer. Tadg is also an ancestor-deity cited in Munster and Leinster pedigrees.
See Standish Hayes O'Grady, Silva Gadelica (2 vols., London, 1892).