John Maynard Keynes, 1st Baron Keynes, CB FBA (5 June 1883–21 April 1946) was a British economist whose ideas have profoundly affected the theory and practice of modern macroeconomics, as well as the economic policies of governments. He greatly refined earlier work on the causes of business cycles, and advocated the use of fiscal and monetary measures to mitigate the adverse effects of economic recessions and depressions. Keynes is widely considered to be one of the founders of modern macroeconomics, and to be the most influential economist of the 20th century. His ideas are the basis for the school of thought known as Keynesian economics, as well as its various offshoots.
In the 1930s, Keynes spearheaded a revolution in economic thinking, overturning the older ideas of neoclassical economics that held that free markets would, in the short to medium term, automatically provide full employment, as long as workers were flexible in their wage demands. Keynes instead argued that aggregate demand determined the overall level of economic activity, and that inadequate aggregate demand could lead to prolonged periods of high unemployment. Following the outbreak of World War II, Keynes's ideas concerning economic policy were adopted by leading Western economies. During the 1950s and 1960s, the success of Keynesian economics resulted in almost all capitalist governments adopting its policy recommendations.
Keynes's influence waned in the 1970s, partly as a result of problems that began to afflict the Anglo-American economies from the start of the decade, and partly because of critiques from Milton Friedman and other economists who were pessimistic about the ability of governments to regulate the business cycle with fiscal policy. However, the advent of the global financial crisis in 2007 caused a resurgence in Keynesian thought. Keynesian economics provided the theoretical underpinning for economic policies undertaken in response to the crisis by Presidents George W. Bush and Barack Obama of the United States, Prime Minister Gordon Brown of the United Kingdom, and other heads of governments.
In 1999, Time magazine included Keynes in their list of the 100 most important and influential people of the 20th century, commenting that: "His radical idea that governments should spend money they don't have may have saved capitalism." In addition to being an economist, Keynes was also a civil servant, a director of the British Eugenics Society, a director of the Bank of England, a patron of the arts and an art collector, a part of the Bloomsbury Group of intellectuals, an advisor to several charitable trusts, a writer, a philosopher, a private investor, and a farmer.