Ken Griffin, 35, President & Founder, Citadel Investment Group ($1 billion)

Kenneth Griffin, the eighth richest American under 40, is one of the most successful and secretive traders in the world.

During his freshman year at Harvard in 1986, he traded stock options out of his dorm room. A year later, he launched a convertible-bond arbitrage fund. This was the beginning of Citadel Investment Group. In 1987, the US stock markets crashed but Griffin made a big packet.

The Citadel Investment Group has now become one of the world's largest hedge funds, accounting for 1 per cent of all trading activity in New York, London, and Tokyo everyday.

Citadel currently manages nearly $9 billion for a wide range of investors.

Photograph: Citadel Investment Group

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