Manfred Stern (also known as Emilio Kléber, Lazar Stern, Moishe Stern, Mark Zilbert) (1896–1954) was a member of the GRU, Soviet military intelligence. He served as a spy in the United States, as a military advisor in China, and gained fame under his nom de guerre as General Kléber, leader of the International Brigade during the Spanish Civil War.
He was born into a Jewish family in Bukovina (now Hlyboka Raion, Chernivtsi Oblast, Ukraine), a province of the Austro-Hungarian Empire on the border between Romania and Ukraine. He studied medicine at the University of Vienna.
Drafted into the Austro-Hungarian army at the beginning of World War I, he was captured by the Tsarist army and taken to a prisoner of war camp in Siberia. Freed by the October Revolution, he became a Bolshevik and joined the Red Army. He led a partisan unit in Siberia against the White Army of Admiral Kolchak and fought in Mongolia against the warlord "bloody" Baron Ungern von Sternberg and his ally, the religious leader Bogd Khan. In 1921 he was elected to the Constituent Assembly of the short-lived Far Eastern Republic.