Alfred Marshall (1842–1924) was a founder—with Léon Walras—of what is termed the neoclassical school of economics. His Principles of Economics, first published in 1890, was the standard introductory textbook for English speaking students for 50 years. An excellent mathematician, Marshall provided new foundations for the analysis of supply and demand by using calculus to formulate the workings of markets and firms, and express key concepts such as Marginal Cost and Marginal Utility
The concepts of Consumer Surplus and Producer Surplus are also due to Marshall. His conception of economics as an attempt to ‘understand the influences exerted on the quality and tone of a man’s life by the manner in which he earns his livelihood …’ is close to our own definition of the field.