Irving Fisher

He had the intellect to use mathematics in virtually all his theories and the good sense to introduce it only after he had clearly explained the central principles in words. Although he damaged his reputation by insisting throughout the Great Depression that recovery was imminent, contemporary economic models of interest and capital are based on Fisherian principles. Similarly, monetarism is founded on Fisher’s principles of money and prices. [The image comes from “The Warren J. Samuels Portrait Collection at Duke University.”]