Niall Noigiallach aka "Niall of the Nine Hostages" (d450/455 ad.) was one of the greatest Irish kings. He was said to have consolidated his power by leading raids on the Roman Empire, taking hostages from rival Irish royal families, Britain and the European mainland, thus earning the name "Niall of the Nine Hostages" Saint Patrick was said to have been kidnapped and brought to Ireland as one of his hostages during his raids.

Researchers indicate that there could be as many as 3 million descendents of Niall alive today. Most of his descendents are concentrated in northwest Ireland, an area where DNA testing has shown that one in every five males have inherited his Y-chromosome. Studies also show that outside of Ireland, approximately one in 10 men in western and central Scotland also carry the gene, and 2% of European American New Yorkers carried it as well, likely due to the historically high rates of Irish emigration to North America.

Prior to the genetic evidence, there had been doubts that Niall actually existed since he existed prior to written records and he was often considered a mythological figure. Sources for his existence as a historical king come from Lebor Gabala Erenn, Annals of the Four Masters, and chronicles and legendary tales such as the Adventure of the Sons of Eochaid Mugmedon, and The Death of Niall of the Nine Hostages. However, the genetic evidence confirms ancient fables about Niall and suggests that he may be the forefather of approximately 3 million men in the world today.