Short answers, pulled from the story.
John Maynard Keynes (1883-1946) was an English economist whose ideas form the basis of Keynesian economics and its offshoots. He has been called the "father of macroeconomics" and is considered one of the most influential economists of the 20th century. Time magazine named him one of its Most Important People of the Century in 1999, reporting that his idea that governments should spend money they don't have may have saved capitalism.
Published in 1936, The General Theory argues that aggregate demand, the sum of consumption and investment, determines the overall level of economic activity. Keynes challenged the classical view that free markets automatically restore full employment, introducing the concept of price stickiness to explain why wages do not adjust freely downward. The book advocated government spending to stimulate demand during periods of high unemployment and is often described as the foundation of modern macroeconomics.
In The Economic Consequences of the Peace (1919), Keynes argued that the reparations imposed on Germany were so severe they would damage not only the German economy but global trade as a whole. He warned that deliberate impoverishment of Central Europe would invite vengeance and eventual catastrophe. His followers later cited the German hyperinflation of 1923 and the rise of the Nazi regime as vindication, though historians such as Ruth Henig have argued the treaty was not in practice as harsh as Keynes claimed.
At the mid-1944 Bretton Woods negotiations, Keynes proposed a common world currency called the bancor, exchangeable with national currencies at fixed rates, to be managed by an International Clearing Union. The plan would have placed equal obligations on surplus and deficit countries to correct trade imbalances. The United States rejected the plan, and the resulting World Bank and IMF were founded along lines closer to the American negotiator Harry Dexter White's more conservative proposals.
Keynesian economics was undermined by stagflation, the simultaneous rise of unemployment and inflation in the US and Britain in the early 1970s, a combination Milton Friedman had predicted Keynesian policies could produce. Friedman's 1963 A Monetary History of the United States and his 1968 paper on the Phillips curve provided theoretical ammunition, and the 1973 oil crisis worsened conditions. By 1979 the British Government had officially discarded Keynesian economics in favour of monetarism.
Keynes began his career as a committed free trader close to Alfred Marshall. From the 1929 crisis onward he shifted toward protectionism, proposing tariffs on imports to the Macmillan Committee on the 5th of November 1929 and calling for a uniform ten percent tariff in 1930. In his 1933 article National Self-Sufficiency he argued for a degree of national economic self-reliance, criticising the assumptions of Ricardian comparative advantage as unrealistic and potentially wasteful of national resources.