John Maynard Keynes, 1st Baron Keynes, was an English economist and philosopher whose ideas fundamentally changed the theory and practice of macroeconomics and the economic policies of governments. Originally trained in mathematics, he built on and greatly refined earlier work on the causes of business cycles. One of the most influential economists of the 20th century, he produced writings that are the basis for the school of thought known as Keynesian economics, and its various offshoots. His ideas, reformulated as New Keynesianism, are fundamental to mainstream macroeconomics. He is known as the "father of macroeconomics".

John Maynard Keynes was born in Cambridge, England, in June 1883 to an upper-middle-class family. His father, John Neville Keynes, was an economist and a lecturer in moral sciences at the University of Cambridge and his mother, Florence Ada Keynes, a local social reformer. Keynes was the first born, and was followed by two more children – Margaret Neville Keynes in 1885 and Geoffrey Keynes in 1887. Geoffrey became a surgeon and Margaret married the Nobel Prize-winning physiologist Archibald Hill.