The Kelly criterion is a formula used to determine the optimal size of a series of bets, whether in a casino or on the stock market. The theory was put into practice by gamblers like Thorp and Kelly’s associate Claude Shannon, though Kelly himself never used the theory to profit himself – though perhaps he never got the chance. Kelly died in 1965 at only 41 years old, leaving behind a formula that has been used to make the fortunes of big business moguls like Warren Buffet, Bill Gross, and Jim Simons as a legacy.