Russian philosophy has been greatly influential—with contributions from Alexander Herzen, who is known as the "father of Russian socialism"; Mikhail Bakunin, who is referred to as the father of anarchism; Peter Kropotkin, Mikhail Bakhtin, Helena Blavatsky, Vladimir Lenin, who is one of the world's most popular revolutionaries, and developed the political ideology of Leninism; Leon Trotsky, who is the founder of Trotskyism; and Petr Chaadaev, who influenced both the Westernizers and the Slavophiles. Notable Russian philosophers of the late 19th and 20th centuries including Vladimir Solovyov, Alexander Zinoviev, Sergei Bulgakov, Pavel Florensky, Lev Shestov, and Nikolai Berdyaev.