John Maynard Keynes was a British economist who is recognized as the founder of Keynesian economics in the early 20th century. His economic theories aimed to identify and explain the sources of economic growth and propose solutions to government problems of unemployment and inflation. Keynesian economics is based on the idea that demand drives supply, meaning that the demand for goods and services creates the economy's supply of jobs and consumer spending. During economic recessions, when consumer demand is low and unemployment is high, Keynes argued for increased government spending on areas such as infrastructure and public services in order to stimulate consumer demand and create jobs. He argued that such spending could be financed by borrowing or taxing, even if it meant going into debt.

Keynes' economic theories were highly influential in the 1930s, when they were used to address the economic problems of the Great Depression. His theories influenced post-war economic policy in the United Kingdom and many other countries; for instance, the United States adopted Keynesian policies in the 1940s and 1950s. These policies were continued during the Cold War era and even the present day, with the implementation of fiscal stimulus packages to address economic imbalances.

Despite his influence, Keynesian policies are often criticized by economists who argue that they can lead to excessive government spending, overwhelming public debt, and runaway inflation. They also contend that this approach stifles private investment as businesses become frustrated by increases in taxes or a lack of incentives to invest. Supporters of Keynesian economics maintain that these policies are necessary to ensure the health of the economy and to raise the standard of living of people.