Millions of Irish Americans, especially those in New York, might be directly descended from Niall of the Nine Hostages, the most prolific warrior in Irish history.

A team of geneticists at Trinity College Dublin led by Professor Dan Bradley discovered that as many as 3 million men worldwide may be descendants of the Irish warlord, who was the Irish “High King” at Tara, the ancient center of Ireland from A.D. 379 to A.D. 405.

The legend of Niall of the Nine Hostages

The story of Niall of the Nine Hostages is already the stuff of legend, passed on to countless Irish schoolchildren over the years.

The supposedly fearless leader battled the English, the Scots, the French, and even the Romans, and struck fear into the heart of his enemies. His dynasty lasted for centuries, continuing up until the Elizabethan conquest of Ireland at the end of the 16th century.

Legend has it that it was Niall of the Nine Hostages who, on a raid in Wales, captured a young slave and brought him to Ireland. That slave would later escape and go to become Ireland’s patron saint, St. Patrick.

But one story not told to most Irish elementary schoolchildren was Niall’s prolificacy.

When it came to the bedroom, it seems that Niall of the Nine Hostages was even more fearless and energetic than he was on the battlefield.

This warlord was responsible for the very common Irish surname “O’Neill” (“Ui Neill” in Gaelic), which literally means ‘descendant son of Niall.'

One in 12 men in Ireland

The researchers also found that as many as one in 12 men in Ireland have the same DNA as the Irish king and in Ireland’s northwest, that figure rises to one in five.

"We sampled 60 people with these names and found the strongest association was with them,” Bradley told the UK Independent in 2006.

“Before this, everything was mythology, but now there does seem to have been a single male ancestor of this group of powerful dynasties."

"In many countries, powerful men historically have more children, and it's not that hard to believe that it happened in Ireland too.

"We estimate there are maybe two to three million descendants in the modern age, with a concentration in Ireland, obviously. Then there are Scotland and New York  - you find the particular chromosome in reasonable frequency in New Yorkers of European descent.”

IrishCentral History

Love Irish history? Share your favorite stories with other history buffs in the IrishCentral History Facebook group.

1 in 50 New Yorkers who have European roots 

That means that around one in 50 New Yorkers who have European roots – with surnames such as O'Connor, Flynn, Egan, Hynes, O'Reilly, and Quinn – have the same genetic signature as Niall of the Nine Hostages, Bradley said.

This prompted Peter Quinn, the renowned Irish American author from the Bronx, to tell the New York Times, "I hope this means that I inherit a castle in Ireland."

* Originally published in 2009, updated in July 2024.