Joseph Zack Kornfeder (1898–1963), sometimes surnamed "Kornfedder" in the press, was an Austro-Hungarian-born American who was a founding member and top leader of the Communist Party of America in 1919, Communist Party USA leader, and Comintern representative to South America (1930-1931) before quitting the Party in 1934. After his wife was arrested by the secret police during the Great Terror (1937-1938), Zack became a vehement Anti-Communist and testified before the Dies Committee (1939) and Canwell Committee (1948).