Vladimir Ilyich Lenin was a Russian revolutionary, politician, and political theorist who played a key role in the establishment of the Soviet Union. He was the leader of the Bolshevik Party and led the October Revolution of 1917, which resulted in the overthrow of the Russian Provisional Government and the establishment of a socialist state. Lenin served as the head of government of Soviet Russia from 1917 to 1924 and then as the leader of the Soviet Union until his death. He is known for his contributions to Marxist theory, particularly his development of the concept of vanguardism and his advocacy for a proletarian revolution.