William F. Sharpe is an American economist best known for his work in finance and investment theory. He was awarded the Nobel Prize in Economic Sciences in 1990 for developing the Capital Asset Pricing Model (CAPM), which helps investors understand the relationship between risk and expected return. Sharpe also created the Sharpe Ratio, a measure used to evaluate the performance of an investment by adjusting for its risk. His contributions have significantly influenced modern portfolio theory and investment management, making him a key figure in the field of finance.