Alfred Marshall was one of the most influential economists of his time. In 1885 he became Professor of Political Economy at the University of Cambridge, where he remained until his retirement in 1908.
His book, Principles of Economics (1890), was the dominant economic textbook in England for many years. It brings the ideas of supply and demand, marginal utility, and costs of production into a coherent whole.
Marshall is considered as one of the founders of neoclassical economics. Although he took economics to a more mathematically rigorous level, he did not want mathematics to overshadow economics and thus make economics irrelevant to the layman.