Nath Í mac Fiachrach

Nath Í, also known as Dathí, son of Fiachrae, son of Eochaid Mugmedon, was a semi-historical Irish king of the 5th century, the father of the likely-historical king Ailill Molt and the ancestor of the Uí Fiachrach dynasties of early medieval Connacht. According to legend, he was a High King of Ireland, and died after being struck by lightning while on an expedition to the Alps.

Historically, Nath Í is primarily known for his descendants. His son Ailill Molt was likely a historical 5th century king. Two more sons, Echu and Fiachnae, were the ancestors of the Uí Fiachrach Aidni and the Uí Fiachrach Muaide respectively, both early medieval dynasties in Connacht. A fourth son, Amalgaid, was the ancestor of Tírechán, the 7th century bishop and biographer of St. Patrick.

Nath Í's own status and position are disputed. Most early Irish sources, including the Lebor Gabála Érenn, the Annals of the Four Masters and Geoffrey Keating's Foras Feasa ar Éirinn, place him in the traditional list of High Kings of Ireland, after Niall of the Nine Hostages and before Niall's son Lóegaire, with Nath Í's son, Ailill Molt, succeeding Lóegaire. However, he is not included in the earliest list of kings of Tara, the Baile Chuinn Chétchathaig.T. F. O'Rahilly argues that Nath Í did not rule at Tara, but was in fact a king of the province of Connacht, although he accepts that Ailill Molt was a king of Tara. However, Nath Í's name does not appear on the Connacht regnal lists, and Ailill Molt's does.T. M. Charles-Edwards considers it a possibility that neither were kings of Tara, but that both were included later, when members of the Uí Fiachrach dynasties were prominent and it was felt politically necessary to include their ancestors in the ranks of former High Kings.

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