Linda A. Cicero / Stanford News Service · CC BY 3.0

An economist whose "impossibility theorem" proved something genuinely unsettling: that no voting system can convert individual preferences into a coherent collective ranking while satisfying a small set of reasonable fairness conditions. He also did foundational work on general equilibrium theory, showing under what conditions a market economy can settle into a stable set of prices. He won the Nobel Memorial Prize in Economic Sciences in 1972, and four of his doctoral students went on to win it themselves.