Emil Julius Klaus Fuchs (December 29, 1911 – January 28, 1988) pronounced Fu'cks was a German-born theoretical physicist and atomic spy who was convicted of surreptitiously supplying information on the British and American atomic bomb research to the USSR during, and shortly after, World War II. Fuchs was an extremely competent scientist, responsible for many significant theoretical calculations relating to the first fission weapons and early models of the hydrogen bomb while a physicist at Los Alamos National Laboratory.