John Maynard Keynes, 1st Baron Keynes (pronounced /ˈkeɪnz/) (5 June 1883 – 21 April 1946) was a renowned economist from Britain whose many ideas on economic and political theories as well as on many governments' monetary policies influenced America. He advocated a government that played an active role in the lives of people regarding business, economy, etc. In this role, the government would use fiscal measures to reduce the consequences of recessions, economic depressions and booms. His ideas are the basis for the school of thought known as Keynesian economics.

Keynes was to spearhead a revolution in economic thinking overturning the older ideas which held that free markets would certainly allow full employment for all workers who agreed to lower their demands for higher wages. Shortly before the end of the Great Depression his ideas were wholeheartedly put into practice by leading Western economies. During the 1950s and 60s, the success of Keynesian economics was so resounding that almost all capitalist governments around the globe utilized its policies. President Nixon went as far as to declare "We are all Keynesians now". Keynes's ideas became less influential in the 1970s, after attacks from Milton Friedman and other economists who were less optimistic than Keynes about the potential for interventionist government policy to complement the free market. But in 2008 Keynes's ideas enjoyed a revival, with Keynesian thinking being behind the plans of President Barack Obama and other global leaders to rescue America's treasury and economy.

Time Magazine named Keynes one of 100 most influential people of the 20th century and reported "His radical idea that governments should spend money they don't have may have saved capitalism". He is one of the fathers of modern theoretical macroeconomics.