From Reuters.com:
Scientists discover most fertile Irish male
Tue Jan 17, 2006
By Siobhan Kennedy
DUBLIN (Reuters) - Scientists in Ireland may have found the country's most fertile male, with more than 3 million men worldwide among his offspring.
The scientists, from Trinity College Dublin, have discovered that as many as one in twelve Irish men could be descended from Niall of the Nine Hostages, a 5th-century warlord who was head of the most powerful dynasty in ancient Ireland.
His genetic legacy is almost as impressive as Genghis Khan, the Mongol emperor who conquered most of Asia in the 13th century and has nearly 16 million descendants, said Dan Bradley, who supervised the research.
[snip]
[Read the whole story]

Wow, that's pretty interesting about both men. This is one of the reasons I find genealogy so fascinating.