American economist, Nobel laureate (1976), and the most effective public advocate of free-market economics in the second half of the 20th century. Based at Chicago for most of his career, Friedman was the central figure in the "Chicago school" that challenged Keynesian orthodoxy and helped reshape economic policy from the late 1970s onward.
His technical contribution was monetarism — developed in A Monetary History of the United States, 1867–1960 (1963, with Anna Schwartz) — which argued that variations in the money supply are the dominant driver of short-run nominal income, and that the Great Depression was not a failure of markets but a catastrophic failure of the Federal Reserve, which allowed the money stock to collapse by a third. The implication was that discretionary fiscal policy (Keynes's prescription) is less necessary and less reliable than Keynesians believed; a central bank following a stable monetary rule could, in principle, manage the business cycle on its own. The 1970s stagflation — high inflation and high unemployment, which Keynesian models struggled to explain — handed his framework the moment it needed.
His political writing was more sweeping. Capitalism and Freedom (1962) and the PBS series Free to Choose (1980) argued that economic freedom (free markets, competition, limited government) is a necessary condition of political freedom, and that a long list of well-meaning programs (occupational licensing, rent control, public schooling monopolies, drug prohibition) produce predictable and perverse consequences. He advised Reagan, Thatcher, and — more controversially — Pinochet's Chile, drawing lifelong criticism for the last.
With Friedrich A. Hayek, he is the 20th-century intellectual pillar of what eventually came to be called Neoliberalism.