Joseph Stalin rose through the Bolshevik underground in the Russian Empire, organizing party activity and spending repeated periods under arrest or in exile. After the 1917 revolutions he entered the new government's leadership and served as commissar for nationalities. Appointment as Communist Party general secretary in 1922 gave him power over personnel and organization. Following Lenin's death in 1924, he defeated successive rivals through shifting alliances, ideological campaigns and control of the party apparatus, eventually establishing a personal dictatorship.

From the late 1920s Stalin imposed rapid industrialization and forced collectivization of agriculture. State planning expanded heavy industry, but coercive procurement, dispossession and the attack on peasants classified as kulaks brought enormous suffering. Famine killed millions, especially in Ukraine, Kazakhstan and other regions; policies and their implementation were central to the catastrophe. The security police and labour camps enforced repression. During the Great Terror of 1936–1938, fabricated conspiracies, show trials and mass operations led to executions and imprisonment on a vast scale, including within the military and party.

The 1939 pact with Nazi Germany included a secret division of eastern Europe into spheres of influence. Soviet occupation, deportations and killings followed in acquired territories. Germany's invasion in June 1941 exposed the consequences of earlier strategic misjudgements and military purges. Stalin nevertheless directed a mobilized state whose forces, after immense losses, played the principal role in defeating Germany on the eastern front. Victory depended on soldiers, civilians, commanders, industrial relocation and Allied support; it did not erase the costs of his decisions. Wartime deportations of entire national groups added another major crime of the regime.

At Yalta and Potsdam he negotiated from the position created by Soviet military power. Postwar control over eastern European governments, rivalry with western powers and renewed domestic repression helped shape the Cold War. His administration continued persecution and ideological campaigns, including increasingly antisemitic measures near the end of his life. He died in March 1953. The subsequent leadership exposed parts of his record, but many institutions and practices persisted. His rule transformed Soviet power through mass violence, while propaganda concealed the costs of dictatorship.