Someone who is a follower of Bolshevism. Along with Menshevism, these constituted the two branches of Russian socialism from 1903 until Lenin emerged as undisputed leader in the Russian Civil War of 1918-20.

The name arose from the Russian Social Democratic Labor party, which convened secretly in Minsk in 1898, and later in Brussels and then London in 1903. Lenin's party had a majority, and were therefore known as Bolsheviki (members of the majority), while Menshevik meant those who were in the minority.

Lenin's party favored a small class of professional revolutionaries to take over power, while the Mensheviks favored a more open and loosely organized party. The Bolsheviks also favored rule by the proletariat, while the Mensheviks favored an intermediate rule by the bourgeois. While both participated on the same side in the Russian Revolution of 1905, they later split into separate parties until the Mensheviks were suppressed in 1921. Leon Trotsky was originally a Menshevik, but later switched to the Bolshevik camp.