Joseph Vissarionovich Stalin (born Dzhugashvili; 18 December [O.S. 6 December] 1878 – 5 March 1953) was a Soviet politician and revolutionary who led the Soviet Union from 1924 until his death in 1953. He held office as General Secretary of the Communist Party from 1922 to 1952 and as premier from 1941 until his death. Despite initially governing the country as part of a collective leadership, he eventually consolidated power to become a dictator by the 1930s. Stalin codified the party's official interpretation of Marxism as Marxism–Leninism, and his version of it is referred to as Stalinism.

Born into a poor Georgian family in Gori, Russian Empire, Stalin attended the Tiflis Theological Seminary before joining the Marxist Russian Social Democratic Labour Party. He raised funds for Vladimir Lenin's Bolshevik faction through bank robberies and other crimes, and edited the party's newspaper, Pravda. He was repeatedly arrested and underwent several exiles to Siberia. After the Bolsheviks seized power in the October Revolution of 1917, Stalin served as a member of the Politburo, and from 1922 used his position as General Secretary to gain control over the party bureaucracy. After Lenin's death in 1924, Stalin won the leadership struggle over rivals including Leon Trotsky. Stalin's doctrine of socialism in one country became central to the party's ideology, and his five-year plans starting in 1928 led to forced agricultural collectivisation, rapid industrialisation, and a centralised command economy. His policies contributed to a famine in 1932–1933 which killed millions, including in the Holodomor in Ukraine. Between 1936 and 1938, Stalin executed hundreds of thousands of his real and perceived political opponents in the Great Purge. Under his regime, an estimated 18 million people passed through the Gulag system of forced labour camps, and more than six million people, including kulaks and entire ethnic groups, were deported to remote areas of the country.

Stalin promoted Marxism–Leninism abroad through the Communist International and supported European anti-fascist movements. In 1939, his government signed the Molotov–Ribbentrop Pact with Nazi Germany, enabling the Soviet invasion of Poland at the start of World War II. Germany broke the pact by invading the Soviet Union in 1941, leading Stalin to join the Allies. The Red Army, with Stalin as its commander-in-chief, repelled the German invasion and captured Berlin in 1945, ending the war in Europe. The Soviet Union established Soviet-aligned states in Eastern Europe, and with the United States emerged as a global superpower, with the two countries entering a period of rivalry known as the Cold War. Stalin presided over post-war reconstruction and the first Soviet atomic bomb test in 1949. During these years, the country experienced another famine and a state-sponsored antisemitic campaign culminating in the "doctors' plot". In 1953, Stalin died after a stroke. He was succeeded as leader by Georgy Malenkov and eventually Nikita Khrushchev, who in 1956 denounced Stalin's rule and began a campaign of "de-Stalinisation".

One of the 20th century's most significant figures, Stalin has a deeply contested legacy. During his rule, he was the subject of a pervasive personality cult within the international Marxist–Leninist movement, which revered him as a champion of socialism and the working class. Since the dissolution of the Soviet Union in 1991, Stalin has retained a degree of popularity in some of the post-Soviet states (particularly Russia and Georgia) as an economic moderniser and victorious wartime leader who transformed the Soviet Union into an industrialised superpower. Conversely, his regime has been widely condemned for overseeing mass repression and man-made famine which resulted in the suffering and deaths of millions of Soviet citizens.

Stalin was born on 18 December [O.S. 6 December] 1878 in Gori, Georgia, then part of the Tiflis Governorate of the Russian Empire. An ethnic Georgian, his birth name was Ioseb Besarionis dze Jughashvili (Russified as Iosif Vissarionovich Dzhugashvili). His parents were Besarion Jughashvili and Ekaterine Geladze; Stalin was their third child and the only one to survive past infancy. After Besarion's shoemaking workshop went into decline, the family fell into poverty, and he became an alcoholic who beat his wife and son. Ekaterine and her son left the home by 1883, moving through nine different rented rooms. In 1888, Stalin enrolled at the Gori Church School where he excelled. He faced health problems: an 1884 smallpox infection left him with facial scars, and at age 12 he was seriously injured when he was struck by a phaeton, causing a lifelong disability in his left arm.

In 1894, Stalin enrolled as a trainee Russian Orthodox priest at the Tiflis Theological Seminary, enabled by a scholarship. He initially achieved high grades, but lost interest in his studies. Stalin became influenced by Nikolay Chernyshevsky's pro-revolutionary novel What Is To Be Done?, and Alexander Kazbegi's The Patricide, with Stalin adopting the nickname "Koba" from its bandit protagonist. After reading Das Kapital, Stalin focused on Karl Marx's philosophy of Marxism, which was on the rise as a variety of socialism opposed to the Tsarist authorities. He began attending secret workers' meetings, and left the seminary in April 1899.

During October 1899, he worked as a meteorologist at the Tiflis observatory. He attracted a group of socialist supporters, and co-organised a secret workers' meeting where he convinced many to strike on May Day 1900. The empire's secret police, the Okhrana, became aware of Stalin's activities and attempted to arrest him in March 1901, but he went into hiding during which he lived off donations from friends. He helped plan a demonstration in Tiflis on May Day 1901 at which 3,000 marchers clashed with the authorities. Stalin was elected to the Tiflis Committee of the Russian Social Democratic Labour Party (RSDLP) –a Marxist party founded in 1898– in November 1901.

That month, he travelled to Batumi. His militant rhetoric proved divisive among the city's Marxists, some of whom suspected that he was an agent provocateur. Stalin began working at the Rothschild refinery storehouse, where he co-organised two workers' strikes. After the strike leaders were arrested, he co-organised a mass demonstration which led to the storming of the prison. Stalin was arrested in April 1902 and sentenced to three years exile in Siberia, arriving in Novaya Uda in November 1903. After one failed attempt, Stalin escaped from his exile in January 1904 and travelled to Tiflis, where he co-edited the Marxist newspaper Proletariatis Brdzola ("Proletarian Struggle") with Filipp Makharadze. During his exile, the RSDLP had become divided between Vladimir Lenin's "Bolshevik" faction and Julius Martov's "Mensheviks". Stalin, who detested many Mensheviks in Georgia, aligned himself with the Bolsheviks.