28. LUKAS WALTON

$18.1  SELF-MADE SCORE: !

BILLION SOURCE: WALMART AGE: 33 RESIDENCE: JACKSON, WY PHILANTHROPY SCORE: He inherited a stake in Walmart when his father, John, son of founder Sam Walton, died in a plane crash in 2005. He studied environmentally sustainable business at Colorado College and now invests in eco-friendly funds. He has donated at least $149 million to the Walton Family Foundation.