Genrikh Yagoda in the context of "NKVD"

The Great Purge or Great Terror (Russian: Большой террор, romanized: Bol'shoy terror), also known as the Year of '37 (37-й год, Tridtsat' sed'moy god) and the Yezhovshchina (ежовщина [(j)ɪˈʐofɕːɪnə], lit. 'period of Yezhov'), was a political purge in the Soviet Union from 1936 to 1938. After the assassination of Sergei Kirov by Leonid Nikolaev in 1934, Joseph Stalin launched a series of show trials known as the Moscow trials to remove suspected dissenters from the Communist Party of the Soviet Union (especially those aligned with the Bolshevik party). The term "great purge" was popularized by historian Robert Conquest in his 1968 book, The Great Terror, whose title alluded to the French Revolution's Reign of Terror.

The purges were largely conducted by the NKVD (People's Commissariat for Internal Affairs), which functioned as the interior ministry and secret police of the USSR. In 1936, the NKVD under Genrikh Yagoda began the removal of the central party leadership, Old Bolsheviks, government officials, and regional party bosses. Soviet politicians who opposed or criticized Stalin were removed from office and imprisoned, or executed, by the NKVD. The purges were eventually expanded to the Red Army high command, which had a disastrous effect on the military. The campaigns also affected many other segments of society: the intelligentsia, wealthy peasants—especially those lending money or other wealth (kulaks)—and professionals. As the scope of the purge widened, the omnipresent suspicion of saboteurs and counter-revolutionaries (known collectively as wreckers) began affecting civilian life.

The Case of the Anti-Soviet "Bloc of Rightists and Trotskyites" (or "Bloc of Rights and Trotskyites"; Russian: Процесс антисоветского «право-троцкистского блока»), also known as the Trial of the Twenty-One, was the last of the three public Moscow trials charging prominent Bolsheviks with espionage and treason. The Trial of the Twenty-One took place in Moscow in March 1938, towards the end of the Soviet Great Purge. The accused were tortured to extract confessions and publicly admitted their guilt during the show trial. Most of the accused, including Nikolai Bukharin, Alexei Rykov and Genrikh Yagoda, were convicted, and sentenced to death. All charges are considered fabricated except the against NKVD chief Genrikh Yagoda of poisoning Valerian Kuybyshev, Vyacheslav Menzhinsky, and Maxim Gorky; Yagoda might indeed have conducted the poisoning with the assistance of "Kremlin's doctors" Pletnyov and Lev Levin, but they did it on the orders from Stalin himself.