226. John Arnold
$3.3 billion self-made score: * source: Hedge funds age: 43 residence: Houston B.a., vanderbilt, ’95 Arnold shocked the hedge fund world in 2012 when, at just 38 years old, he announced he was retiring. A former Enron trader, he went on to build his own hedge fund, minting a fortune. Arnold has since focused on what he calls “strategic” philanthropy. His initiatives include tackling “bad science” by pushing for academic studies that are more rigorously data-driven and funding criminal-justice reform efforts, including testing the impact of police body cameras on public safety.