Austrian-born economist and political philosopher, dominant figure of the "Austrian school" after Mises, and the most intellectually serious defender of market liberalism in the 20th century. Hayek's core insight — developed in essays like The Use of Knowledge in Society (1945) — is epistemic: the information required to coordinate a modern economy (who wants what, at what cost, with what substitutes) is irretrievably dispersed across millions of people and mostly tacit, unwritable, and local. Markets, through the price mechanism, aggregate and communicate this knowledge in real time in ways no central planner can match. Socialist calculation therefore fails not (only) because planners are bad but because the task is in principle impossible.
The Road to Serfdom (1944), written during WWII, warned that comprehensive economic planning — even well-intentioned — would erode political liberty by concentrating the power to direct people's lives. The argument helped make Hayek a political figure (and, later, a patron saint of Thatcher and Reagan, to his occasional discomfort). His mature political theory in The Constitution of Liberty (1960) and the three-volume Law, Legislation and Liberty (1973–79) developed a distinction between "cosmos" (spontaneous order — language, common law, markets) and "taxis" (deliberately designed order). Good societies lean heavily on cosmos; attempts to design cosmos from scratch destroy what they try to replace.
Hayek is often grouped with Robert Nozick as a libertarian, but he was actually closer to Michael Oakeshott in temperament — a classical liberal suspicious of ideologues of every kind, including free-market ones.