Soviet Communist leader, originally named Radomyslsky. He joined the Russian Social Democratic Labour party in 1901 and sided with Vladimir Lenin's Bolshevik faction after 1903 (see Bolsheviks).
Zinoviev conducted agitation in St. Petersburg during the 1905 revolution and was elected to the central committee of the party in 1907. After a brief period in jail, he went abroad in 1908.
Zinoviev was one of Lenin's closest collaborators in exile (1909-1917) and returned to Russia with him after the February 1917 revolution.
After the Bolshevik take-over, Zinoviev served as head of the Comintern (1919 - 1926). On Lenin's death (1924), Zinoviev, Kamenev, and Stalin formed a ruling triumvirate. Zinoviev led the triumvirate's attack on Lev Trotsky, calling for his expulsion from the party.
After an initial victory over Trotsky (1924), Stalin, in an effort to consolidate his own power, turned against Zinoviev and Kamenev, defeating them and their so-called left opposition in 1925. Zinoviev and Kamenev then allied themselves with Trotsky (1926), but to no avail. Zinoviev was removed from his party posts in 1926 and expelled from the party in 1927. He recanted and was readmitted in 1928 but wielded little influence.
Many features of the Zinoviev-Kamenev program, emphasising rapid industrialisation and collectivisation, were incorporated (1928) in Stalin's first Five-Year Plan.
In 1935, Zinoviev was sentenced to 10 years' imprisonment purportedly for giving his encouragement to the assassins of Sergei Kirov. Accused (1936) of conspiring to overthrow the government, he was the chief defendant in the first of the trials held by Stalin, which resulted in Zinoviev's execution along with Kamenev and 13 other old Bolsheviks.
In 1988, he was posthumously rehabilitated and the verdict of his show trial was annulled by the Soviet supreme court. The so-called Zinoviev letter was published (1924) in the British press. It was allegedly written by Zinoviev in his capacity as Comintern chief and contained instructions for Communist revolution in England. Although a forgery, the Zinoviev letter helped to defeat Britain's first Labour government in elections that year.