4. John Grayken

Boston-born John Grayken (63) is unlikely to have known what opportunities Ireland would present for his private equity firm when he renounced his US citizenship for tax purposes in 1999 and took Irish citizenship.

He is the founder and chairman of Lone Star, which became a household name during the recession due to its vulture fund status. Grayken’s modus operandi is to buy distressed property assets in countries experiencing economic turmoil, clean them up and flip the assets for a profit. He made a fortune in Japan and South East Asia during the late 1990s.