Feller, William (1906–1970)

Yugoslavian-born US mathematician. He is largely responsible for making the theory of probability accessible to students of subjects other than mathematics through his textbook on the subject. In the theory of limits, he formulated the law of the iterated logarithm.

Feller came to the conclusion, early on, that the traditional emphasis placed on averages meant that insufficient attention was paid to random fluctuations. Much of his study of probability theory focused on the nature of Markov processes (a mathematical description of random changes in a system which, for instance, can occur in either of two states). Feller demonstrated the applicability of this tool to subjects in which probability theory had not usually previously been employed; for example, in the study of genetics. His work is set out in Introduction to Probability Theory and its Applications (1950–66).

Feller was born and educated in Zagreb and also studied in Germany at Göttingen. He worked at the University of Stockholm 1933–39. On the outbreak of World War II, he emigrated to the USA. He was professor of mathematics at Cornell University, New York, 1945–50, and at Princeton from 1950.