John Maynard Keynes, Baron Keynes of Tilton, 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. His ideas are the basis for the school of thought known as Keynesian economics, as well as its various offshoots.
Keynes is widely considered to be one of the founders of modern macroeconomics, and to be the most influential economist of the 20th century. 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 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 private investor, and a farmer.
Source: Wikipedia, "John Maynard Keynes", available under the CC-BY-SA License.