Founding father of the USSR. Vladimir Ilyich Ulyanov, better known by his alias Lenin,[c] was a Russian revolutionary, politician, and political theorist. He served as the first and founding head of government of Soviet Russia from 1917 to 1924 and of the Soviet Union from 1922 to 1924. Under his administration, Russia, and later the Soviet Union, became a one-party socialist state governed by the Communist Party. Ideologically a Marxist, he developed a subset of Marxism called Leninism.

After the 1917 February Revolution ousted the Tsar and established a Provisional Government, he returned to Russia to play a leading role in the October Revolution in which the Bolsheviks overthrew the new regime.

Lenin's Bolshevik government initially shared power with the Left Socialist Revolutionaries, elected soviets, and a multi-party Constituent Assembly, although by 1918 it had centralised power in the new Communist Party. Lenin's administration redistributed land among the peasantry and nationalised banks and large-scale industry. It withdrew from the First World War by signing a treaty conceding territory to the Central Powers, and promoted world revolution through the Communist International. Opponents were suppressed in the Red Terror, a violent campaign administered by the state security services; tens of thousands were killed or interned in concentration camps.

His administration defeated right and left-wing anti-Bolshevik armies in the Russian Civil War from 1917 to 1922 and oversaw the Polish–Soviet War of 1919–1921. His health failing, Lenin died in Gorki, with Joseph Stalin succeeding him as the pre-eminent figure in the Soviet government.

Widely considered one of the most significant and influential figures of the 20th century, Lenin was the posthumous subject of a pervasive personality cult within the Soviet Union until its dissolution in 1991. He became an ideological figurehead behind Marxism–Leninism and a prominent influence over the international communist movement. A controversial and highly divisive historical figure, Lenin is viewed by his supporters as a champion of socialism and the working class. Meanwhile Lenin's critics accuse him of establishing a totalitarian dictatorship which oversaw mass killings and political repression.