en.wikipedia.org/wiki/Vasily_Blokhin

Blokhin was selected for the position by Joseph Stalin in 1926 and led a company of executioners that performed and supervised numerous mass killings in the Soviet Union during Stalin’s reign, mostly during the Great Purge and Eastern Front of World War II.[1] Blokhin is recorded as having executed tens of thousands of prisoners by his own hand, including his killing of about 7,000 Polish prisoners of war during the Katyn massacre in spring 1940, making him the most prolific official executioner in recorded world history.[1][2][3] Blokhin was forced into retirement in 1953 after the death of Stalin and condemned during de-Stalinization shortly before his death in 1955.