Who is Viktor Semyonovich Abakumov from The Gulag Archipelago, 1918-1956 and what is their importance?

Stalin's Minister of State Security (1946-52), Abakumov is shown with his deputy, M.D. Ryumin, enjoying beating prisoners on the sciatica nerve with a rubber truncheon in Abakumov's opulent appointed office, taking care not to splatter the Persian carpets. Abakumov raises Ryumin rapidly and they become close, until the end of 1952, when they cross-examine the suspect Etinger (who dies overnight), reach opposite conclusions, and Ryumin is commissioned by Stalin to prosecute the "doctors' case." He arrests Abakumov, but when Stalin dies, the new government arrests and shoots Ryumin. Abakumov resents encroachment on the Organs, warns authorities against opposing him, and taunts them for not letting the Secret Police handle the Beria investigation. He fears poisoning in prison, reads Stalin's works for show, is rumored to have beaten Khrushchev's daughter-in-law to death in Stalin's time, and is finally tried and shot in 1954.