Joseph Stalin was the prominent communist leader of the Soviet Union during World War II. He became General Secretary of the Communist Party in the early 1920s and led the USSR through the war's tumultuous period. Under his rule, the Soviet Union played a critical role in defeating Nazi Germany, particularly through significant battles such as Stalingrad and Kursk. Stalin's leadership had significant implications for post-war Europe, as his policies shaped the USSR's expansion and imposition of communist governments across Eastern Europe, laying the groundwork for the Cold War.