He was involved with Lenin in revolutionary politics in St Petersburg in 1895 and was exiled to a different part of Siberia at the same time as Lenin.
Following his release from exile, he also moved to Switzerland to join Lenin and Plekhanov.
He collaborated with Lenin in the creation of party newspaper Iskra in 1900.
He disagreed with the argument in Lenin's pamphlet "What is to be done?".
Instead, he argued that the SD movement should broaden its support base through trade unions, co-operatives and soviets in order to bring down the tsarist government.