John Maynard Keynes, 1st Baron Keynes, was a British economist whose ideas fundamentally changed the theory and practice of macroeconomics and the economic policies of governments. He built on and greatly refined earlier work on the causes of business cycles, and was one of the most influential economists of the 20th century and the founder of modern macroeconomic theory. His ideas are the basis for the school of thought known as Keynesian economics, and its various offshoots.