Ursynovich Sergey (1891–1935) – historian of religion.

He entered the Faculty of Law of the Moscow University in 1909. After the course, he stayed there to continue his research work. In 1917, he was Ass. Docent at the Moscow University, teaching the Theory of State and Law. In 1918, he taught at the Ivanovo-Voznesensk Pedagogical Institute. For some time, he worked in Saratov. Since the early 1920s, he was again in Moscow, a teacher at the Evening Workers' Faculty named after N. Bukharin (formerly Prechistenskie Courses), which was under the supervision of the People's Commissariat for Education; probably, he taught at other educational institutions in Moscow.

From 1925 to 1935, employee of the Great Soviet Encyclopedia and the Encyclopedia of State and Law. From 1926 to 1935, a member of the Research and Methodological Council of the Union of Militant Atheists, an employee of the magazine ‘Anti-Religious’. From 1928 to 1935, an employee of the Commission on the History of Religion of the Communist Academy (since 1930, the Anti-Religious Section of the Institute of Philosophy). From 1930 to 1933, Ass. Professor of the First Moscow University. From 1933 until his death, Ass. Professor of the Moscow Historical and Philosophical Institute. Since 1930, he has been working at the Museum of Oriental Cultures, the Central Museum of Ethnology, and at the Central Anti-Religious Museum, where in 1935 he prepared an exposition on Buddhism.

He was engaged in field research, including Siberia, where he studied the religion of Nivkhs (Gilyaks), and in Buryat-Mongolia; he studied provincial archives, especially the process of Christianization of the peoples of the Volga Region, the Urals, and Siberia.

Member of the Society of Marxist Historians, member of the Society for the Study of Siberia, the Urals, and the Far East. For 18 years of his research activity, U. has written over 200 articles and books.

He died tragically during a fire in his apartment in Moscow in 1935. He was buried at the Novodevichy Cemetery, next to his relatives.