John Maynard Keynes (1883–1946) was an English economist whose ideas fundamentally changed the theory and practice of macroeconomics and the economic policies of governments. Originally trained in mathematics, he built on and refined earlier work on business cycles. He is widely recognized as one of the most influential economists of the 20th century, producing writings that form the basis for the school of thought known as Keynesian economics, and its various offshoots.