Russian State Archive of Socio-Political History

From the English Wikipedia page

Russian State Archive of Socio-Political History (RGASPI) (Russian: Российский государственный архив социально-политической истории (РГАСПИ)), formerly the Marx-Lenin Institute is a large Russian state archive based in Moscow, which holds pre-1952 archives of the Communist Party of the Soviet Union. It is managed by Rosarkhiv. It was established in 1999 as merger of two other archives, the Russian Centre for the Preservation and Study of Documents of Most Recent History (RTsKhIDNI, Russian: Российский центр хранения и изучения документов новейшей истории (РЦХИДНИ) and the Centre for the Preservation of Documents of Youth Organizations (Russian: Центр хранения документов молодежных организаций (ЦХДМО)). Post-1952 archives of the CPSU are collected in the Russian State Archive of Contemporary History.

The archives include many of the personal papers of major Communist and Soviet leaders, including Nikolai Bukharin, Felix Dzerzhinsky, Lazar Kaganovich, Mikhail Kalinin, Lev Kamenev, Sergei Kirov, Georgy Malenkov, Anastas Mikoyan, V. M. Molotov, Georgi Plekhanov, Joseph Stalin, Leon Trotsky, and Grigory Zinoviev.

More information can be found here and on the Russian Wikipedia page.