Lev Davidovich Trotsky (né Bronstein; 7 November [O.S. 26 October] 1879 – 21 August 1940), better known as Leon Trotsky, was a Russian revolutionary, Soviet politician and political theorist. He was a key figure in the 1905 Revolution, October Revolution of 1917, Russian Civil War, and the establishment of the Soviet Union, from which he was exiled in 1929 before his assassination in 1940. Trotsky and Vladimir Lenin were widely considered the two most prominent figures in the Soviet state from 1917 until Lenin's death in 1924. Ideologically a Marxist and a Leninist, Trotsky's ideas and beliefs inspired a school of Marxism known as Trotskyism.
Trotsky joined the Russian Social Democratic Labour Party in 1898, being arrested and exiled to Siberia for his activities. In 1902 he escaped to London, where he met Lenin. Trotsky initially sided with the Mensheviks against Lenin's Bolsheviks in the party's 1903 schism, but declared himself non-factional in 1904. During the 1905 Revolution, Trotsky was elected chairman of the Saint Petersburg Soviet. He was again exiled to Siberia, but escaped in 1907 and lived abroad.