Today, Ken Griffin is the Chairman, President and CEO of Citadel Investment Group, the Chicago-based hedge fund that has grown into a global investment giant with offices in New York, London, Hong Kong and Tokyo, handling more than $20 billion in investment capital.

A teenage computer whiz from Boca Raton, Florida, Griffin started his first investment fund in his Harvard dorm room, writing his own software to execute a novel arbitrage strategy for trading convertible bonds. A year after graduating, he founded Citadel, with $4.6 million in capital. The new firm grew explosively, nimbly riding the waves of a turbulent market. Time and again, Griffin has turned an adverse market to his advantage. When the bottom dropped out of energy trading with the collapse of Enron, he rushed in where others feared to tread, and Citadel is now a major player in the oil and gas markets. This year, he made a similar foray into the troubled home mortgage sector.

Griffin employs a virtual army of scientists, hired from the top universities—mathematicians, programmers, statisticians, even meteorologists—to carry out the research that informs the firm's trading strategy. While other hedge funds specialize in a single market, Chicago-based Citadel is the only player to hold a dominant position across the board, in bonds, equities, currency and options trading.

While the traditional hedge fund reaches a certain size and then contracts slowly or dies when its founder retires, Griffin plans to build a lasting institution comparable to the great investment banking houses. He has already made a lasting impact on the city of Chicago. A formidable art collector himself (he has paid record prices for paintings by Paul Cézanne and Jasper Johns), he has lent some of his treasures to the Art Institute of Chicago and is building the museum a new wing for modern works. In addition to his benefactions to Chicago’s cultural and educational institutions, he is a major force in the city’s bid for the 2016 Olympics. In his own chosen field of competition, Ken Griffin is already a champion.