11. Mark Zuckerberg, Facebook
Net worth: $19bn ( £12bn)
Controversial social media pioneer Zuckerberg launched Facebook at Harvard University in 2004 and it soon went global. Facebook’s disappointing IPO last year sparked suggestions that the company was facing difficulty, but a mobile advertising push has brought their share-price back on the right track.
12. Steve Ballmer, Microsoft
Net worth: $18bn ( £11.3bn)
Ballmer has been CEO of software giant Microsoft since 2000 but announced last month that he will soon be stepping down.
13. Len Blavatnick
Net worth: $17.8bn ( £11.1bn)
Born in Russia, Blavatnick made his fortune through investments and oil. He has money in everything from aluminium to music, and is involved in a range of philanthropic projects.
14. Phil Knight, Nike
Net worth: $16.3bn ( £10.2bn)
One of the few in this list who didn’t make their fortunes through tech or finance, Knight co-founded and is the chairman of sports apparel firm Nike. He created the firm, originally called Blue Ribbon Sports, with Bill Bowerman in 1964.
15. Michael Dell
Net worth: $15.9bn ( £10bn)
Texan Dell founded computer giant Dell Inc in 1984. In January Dell reached an agreement to delist the firm from the stock exchange in the largest private equity leveraged buyout since the financial crisis.