Who is Nikolai Vasilyevich Krylenko from The Gulag Archipelago, 1918-1956 and what is their importance?

The Chief State Prosecutor (1918-31) and later People's Commissar of Justice, Krylenko plays a central role in Solzhenitsyn's analysis of how the Soviets' system of revolutionary "justice" develops. The author's antipathy for Krylenko comes out repeatedly in remarks and asides about his fall from Stalin's grace in 1938 and execution by the very system he puts together.