Mark Andreyevich Natanson (; party name: Bobrov) (25 December 1850 (N.S. 6 January 1851) – 29 July 1919) was a Russian revolutionary who was one of the founders of the Circle of Tchaikovsky, Land and Liberty and the Socialist-Revolutionary Party. In 1917, he was a leader of the Left Socialist-Revolutionaries, which supported the Bolsheviks during the October Revolution. He was the uncle of Alexander Berkman. Early life Natanson was born in 1850 in Švenčionys, Lithuania to a Lithuanian Jewish family but became a Russian revolutionary. His parents died while he was still young and so he was brought up by his uncle. He graduated from the Kaunas men's grammar school in 1868, studied in St Petersburg at the Medical and Surgical Academy (1868–71) and then at the Institute of Agriculture (1871). Meanwhile, he became involved in radical student politics. Populist movement Together with his first wife, he was one of the organizers of the populist Circle of Tchaikovsky. They opposed the 'nihilistic' tendency of Sergei Nechaev, who believed that any means were acceptable for achieving revolutionary goals. The Circle of Tchaikovsky, on the contrary, preached high morality and self-improvement. In 1869-71 he was arrested and imprisoned in the Peter and Paul Fortress, and in 1872 he was exiled to the Arkhangelsk province. In the same 1872 he converted to Orthodoxy in order to formally marry the noblewoman Olga Alexandrovna Shleisner who followed him into exile. In 1876, Natanson returned to Petrograd. He organized the escape abroad of Peter Kropotkin, a comrade from the Circle of Tchaikovsky. In the same year, he began work on the unification of the Narodnik circles into a single revolutionary organization, which in 1878 was called "Land and Liberty." In December 1876, together with Georgi Plekhanov, he organized a demonstration in Kazan square. In 1877, he was once again arrested and, after serving his term in the Peter and Paul Fortress, he was exiled to Eastern Siberia. Upon returning from exile in 1889, he settled in Saratov, where he got a job on the local railway. After 'Land and Liberty' split, he once again began work on the unification of disparate revolutionary circles. He set himself the goal of uniting the populist, social democratic and liberal movements in the Russian liberation movement. In September 1893, at the constituent congress in Saratov, a single party, 'The People's Will' (Narodnaya Volya), was created. The organization's headquarters were in