Maurice Kraitchik

Maurice Borisovich Kraitchik was a Belgian mathematician and populariser. His main interests were the theory of numbers and recreational mathematics.
He was born to a Jewish family in Minsk. He wrote several books on number theory during 1922–1930 and after the war, and from 1931 to 1939 edited Sphinx, a periodical devoted to recreational mathematics. During World War II, he emigrated to the United States, where he taught a course at the New School for Social Research in New York City on the general topic of "mathematical recreations."
Kraïtchik was agrégé of the Free University of Brussels, engineer at the Société Financière de Transports et d'Entreprises Industrielles (Sofina), and director of the Institut des Hautes Études de Belgique. He died in Brussels.
Kraïtchik is famous for having inspired the two envelopes problem in 1953, with the following puzzle in La mathématique des jeux:
Among his publications were the following:Théorie des Nombres, Paris: Gauthier-Villars, 1922Recherches sur la théorie des nombres, Paris: Gauthier-Villars, 1924La mathématique des jeux ou Récréations mathématiques, Paris: Vuibert, 1930, 566 pagesMathematical Recreations, New York: W. W. Norton, 1942 and London: George Allen & Unwin Ltd, 1943, 328 pages Alignment Charts, New York: Van Nostrand, 1944