Jonas Leib "Leo" Stern was an Austrian-German left-wing political activist. In 1933 he switched his party membership from the Social Democratic Party to the Communist Party. During the fascist ascendancy he participated in the Spanish Civil War as an anti-Franco Interbrigadist and later, in the Great Patriotic War, served as an officer in the Soviet Red Army. Between the two he studied successfully for a higher degree at the University of Moscow, receiving his Habilitation degree in 1940 in return for a dissertation on Contemporary Catholicism.