Niall was the eponymous ancestor of the Ui Neill dynasty, which originated in north-eastern Connacht and was dominant in Ireland until the end of the tenth century. His real name was probably Nel (cloud); the change to Niall may be due to the influence of his epithet Notgiallach (of the nine hostages), referring to nine tributary peoples owing allegiance to him. According to some of the later annals, Niall died in the early fifth century; his actual floruit may have been in the fourth century. There is no firm evidence about Niall’s life, as he predates the period of written history. However, he features prominently in myth and legend.
Niall is said to have been the son of Eochaid Mugmedon and Cairenn, who may have been of British origin. The Echtra mac n-Echach Muigmedoin (which is intended to establish the relative political prestige of the Ui Neill and their Connacht cousins), recounts that Eochaid and his other wife, Mongfind, had four sons—Brian, Fiacha, Ailill, and Fergus—three of whom were the progenitors of the Connacht dynasties of Uf Briuin, Uf Fiachrach, and Uf Ailello. Mongfind resented Niall, and she asked Eochaid to judge between all his sons to determine who was to succeed him. The sons were sent on a hunting expedition, during which each one, in turn, went to a well guarded by an ugly, old woman. She demanded a kiss from each before she would permit him to draw water. Fergus and Brian refused; Fiacha kissed her and the woman foretold that he would visit Tara (two of his descendants, Ailill Molt and Nath I, took the kingship). Niall, however, said that he would lie with her as well as kiss her, whereupon she was transformed into a beautiful woman. She identified herself as "sovereignty" and promised Niall that sovereignty would be his and his children’s forever, save for the two (aforementioned) descendants of Fiacha and Brian Boru. Niall is acknowledged as a king of Tara in all of the extant king lists dating from early eighth century onward.
Niall is assigned two wives: Indiu, daughter of Lugaid mac Oengusa Finn of Dal Fiatach of Ulster, and Rfgnach, daughter of Meda mac Rosa, also of Dal Fiatach. The main tradition identifies Indiu as the mother of Niall’s sons; an alternative account relates that their mother was Rfgnach. Niall is credited with between three and fourteen sons, in sources of differing dates, some of whom were recognized as the progenitors of dynasties. The accretion of additional sons would have followed the absorption of various dynastic groupings into the Uf Neill.
According to the saga of Niall’s death, he was slain, while on an expedition in Scotland, by Eochu mac Ennai Cheinnselaig. Cinaed Ua hArtacain, the tenth-century poet, relates that Niall raided Britain seven times and that he was slain on the last of these raids by Eochu, acting in conjunction with the Saxons. (The reference to the Saxons is almost certainly anachronistic.) Niall is said to be have been buried at Ochan (Faughan Hill in Co. Meath).
