Harry Markowitz

Harry Markowitz worked out, mathematically, why "don't put all your eggs in one basket" is good advice: his modern portfolio theory showed how combining assets that don't move in lockstep can lower a portfolio's risk without sacrificing expected return, formalizing diversification into a tool investors and institutions still use to build portfolios today. The work won him the 1990 Nobel Memorial Prize in Economic Sciences and, earlier, the 1989 John von Neumann Theory Prize. He taught finance for years at UC San Diego's Rady School of Management.