Túathal Techtmar

Túathal Techtmar ("the legitimate"), son of Fíachu Finnolach, was a High King of Ireland, according to medieval Irish legend and historical tradition. He is said to be the ancestor of the Uí Néill and Connachta dynasties through his grandson Conn of the Hundred Battles. The name may also have originally referred to an eponymous deity.

Túathal was the son of a former High King deposed by an uprising of "subject peoples" who returned at the head of an army to reclaim his father's throne. The oldest source for Túathal's story, a 9th-century poem by Mael Mura of Othain, says that his father, Fíacha Finnolach, was overthrown by the four provincial kings, Elim mac Conrach of Ulster, Sanb (son of Cet mac Mágach) of Connacht, Foirbre of Munster and Eochaid Ainchenn of Leinster, and that it was Elim who took the High Kingship. During his rule Ireland suffered famine as God punished this rejection of legitimate kingship. Túathal, aided by the brothers Fiacha Cassán and Findmall and their 600 men, marched on Tara and defeated Elim in battle at the hill of Achall. He then won battles against the Ligmuini, the Gailióin, the Fir Bolg, the Fir Domnann, the Ulaid, the Muma, the Fir Ól nÉcmacht and the Érainn, and assembled the Irish nobility at Tara to make them swear allegiance to him and his descendants.

Later versions of the story suppress the involvement of the provincial nobility in the revolt, making the "subject peoples" the peasants of Ireland. The Lebor Gabála Érenn adds the detail of Túathal's exile. His mother, Eithne Imgel, daughter of the king of Alba (originally meaning Britain, later Scotland), was pregnant when Fíachu was overthrown, and fled to her homeland where she gave birth to Túathal. Twenty years later Túathal and his mother returned to Ireland, joined up with Fiacha Cassán and Findmall, and marched on Tara to take the kingship.

...
Wikipedia