Karl Kautsky (October 18, 1854 - October 17, 1938) was a leading theoretician of social democracy. Furthermore, he is also a significant figure in Marxist history, as he was the editor of the fourth volume of Karl Marx's economic critique, Das Kapital.
Born in Prague, Karl Kautsky was studying history and philosophy at the University of Vienna in 1874, and became a member of the Social Democratic Party of Austria (SPÖ) in 1875. From 1885 to 1890, he spent time in London, where he became a close friend of Friedrich Engels; in 1891, he co-authored the Social Democratic Party of Germany (SPD)'s Erfurt Program together with August Bebel and Eduard Bernstein.
Following the death of Friedrich Engels in 1895, Kautsky became one of the most important and influential theoreticians of socialism, forming the Marxist centre of the party together with August Bebel. He stayed with the party when Rosa Luxemburg and the party's left wing broke with it in 1916 over its support for the First World War (see Spartacist League), but changed his mind in 1917 and left for the Independent Social Democratic Party of Germany (USPD), of which he was a member from up to 1919. In 1922 he re-joined the SPD.
Kautsky was described as a "renegade" by Vladimir Lenin, and he in turn castigated Lenin in his 1934 work Marxism and Bolshevism: Democracy and Dictatorship: "The Bolsheviki under Lenin’s leadership, however, succeeded in capturing control of the armed forces in Petrograd and later in Moscow and thus laid the foundation for a new dictatorship in place of the old Tsarist dictatorship."
Of course, Lenin would agree with this assessment, as he would point to the class nature of the dictatorship: i.e. the dictatorship of the proletariat and poor peasantry versus the dictatorship of the landowners and capitalists.
Karl Kautsky lived in Berlin-Friedenau for many years; his wife, Luise Kautsky, was a close friend of Rosa Luxemburg, who also lived in Friedenau, and today there is a commemorative plaque where Kautsky lived at Saarstraße 14. He died in exile in Amsterdam at age 84.