July 7, 1906–January 14, 1970
BY MURRAY ROSENBLATT
WILLIAM FELLER WAS ONE OF THE major figures in the development of interest and research in probability theory in the United States as well as internationally. He was born in Zagreb, Yugoslavia, on July 7, 1906, the son of Eugen Viktor Feller, a prosperous owner of a chemical factory, and Ida Perc. Feller was the youngest of eight brothers, one of twelve siblings. He was a student at the University of Zagreb (1923-1925) and received the equivalent of a master of science degree there. Feller then entered the University of Göttingen in 1925 and completed his doctorate with a thesis titled “Uber algebraisch rektifizierbare transzendente Kurven.” His thesis advisor was Richard Courant. He left Göttingen in 1928 and took up a position as privat dozent at the University of Kiel in 1928. Feller left in 1933 after refusing to sign a Nazi oath. He spent a year in Copenhagen and then five years (1934-1939) in contact with Harald Cramér and Marcel Riesz in Sweden. On July 27, 1938, he married Clara Nielsen, a student of his in Kiel.
At the beginning of the 20th century the most incisive research in probability theory had been carried out in France and Russia. There was still a lack of effective basis for a mathematical theory of probability. There was a notion of a collective introduced by von Mises, defined as a sequence