Keating states that Niall died a pagan, but after the spread of Christianity in Ireland, his descendants (the Uí Néill) became foremost in promoting and endowing the early Christian Church in Ireland; and nearly 300 of them were canonized as saints.
He was the founding ancestor of the great Uí Néill (O’Neill) royal dynasty that would control most of Ireland for the next 1200 years as kings, chieftains, earls, abbots and bishops.
Even 1600 years after the assassination of King Niall, a surprisingly large percentage of the population of northern and western Ireland remain his posterity.
A study, published in the American Journal of Human Genetics (February 2006 issue), conducted at Trinity College Dublin, revealed that a striking percentage of men in Ireland and Scotland share the same chromosome, suggesting that one in twelve Irishmen are descendants of Niall.
For nearly 700 years, the Uí Néill stronghold was the Grianan Aileach, a massive ring fort still standing atop Greenan Mountain, five miles west of modern day Londonderry (Derry): Curiously, part of Niall’s story occurred in England in 1919.