Lev Davidovich Bronstein (7 November [O.S. 26 October] 1879 21 August 1940), better known as Leon Trotsky (), was a Russian Marxist revolutionary, political theorist and politician. Ideologically a communist, he developed a variant of Marxism which has become known as Trotskyism.

Born to a wealthy Ukrainian-Jewish family in Yanovka (now Bereslavka), Trotsky embraced Marxism after moving to Mykolaiv in 1896. In 1898, he was arrested for revolutionary activities and subsequently exiled to Siberia. He escaped from Siberia in 1902 and moved to London, where he befriended Vladimir Lenin. In 1903, he sided with Julius Martov's Mensheviks against Lenin's Bolsheviks during the Russian Social Democratic Labour Party's initial organisational split. Trotsky helped organize the failed Russian Revolution of 1905, after which he was again arrested and exiled to Siberia. He once again escaped, and spent the following 10 years working in Britain, Austria, Switzerland, France, Spain, and the United States. After the 1917 February Revolution brought an end to the Tsarist monarchy, Trotsky returned from New York via Canada to Russia and became a leader in the Bolshevik faction. As chairman of the Petrograd Soviet, he played a key role in the October Revolution of November 1917 that overthrew the new Provisional Government.

Once in government, Trotsky initially held the post of Commissar for Foreign Affairs and became directly involved in the 19171918 Brest-Litovsk negotiations with Germany as Russia pulled out of the First World War. From March 1918 to January 1925, Trotsky headed the Red Army as People's Commissar for Military and Naval Affairs and played a vital role in the Bolshevik victory in the Russian Civil War of 19171922. He became one of the seven members of the first Bolshevik Politburo in 1919.

After the death of Lenin (January 1924) and the rise of Joseph Stalin, Trotsky gradually lost his government positions; the Politburo eventually expelled him from the Soviet Union in February 1929. He spent the rest of his life in exile, writing prolifically and engaging in open critique of Stalinism. In 1938 Trotsky and his supporters founded the Fourth International in opposition to Stalin's Comintern. After surviving multiple attempts on his life, Trotsky was assassinated in August 1940 in Mexico City by Ramn Mercader, an agent of the Soviet NKVD. Written out of Soviet history books under Stalin, Trotsky was one of the few rivals of Stalin to not be rehabilitated by either Nikita Khrushchev or Mikhail Gorbachev. Trotsky's rehabilitation came in 2001 by the Russian Federation.

The Moscow trials were a series of show trials held by the Soviet Union between 1936 and 1938 at the instigation of Joseph Stalin. They were nominally directed against "Trotskyists" and members of "Right Opposition" of the Communist Party of the Soviet Union. At the time the three Moscow trials were given extravagant titles:

the "Case of the Trotskyite-Zinovievite Terrorist Center" (or Zinoviev-Kamenev Trial, also known as the 'Trial of the Sixteen', August 1936);

the "Case of the Anti-Soviet Trotskyist Center" (or Pyatakov-Radek Trial, January 1937); and

the "Case of the Anti-Soviet "Bloc of Rights and Trotskyites"" (or the Bukharin-Rykov Trial, also known as the 'Trial of the Twenty-One', March 1938).The defendants were Old Bolshevik Party leaders and top officials of the Soviet secret police. Most were charged under Article 58 of the RSFSR Penal Code with conspiring with Imperialist powers to assassinate Stalin and other Soviet leaders, dismember the Soviet Union, and restore capitalism. Several prominent figures (such as Andrei Bubnov, Alexander Beloborodov, Nikolay Yezhov) were sentenced to death during this period outside these trials.

The Moscow trials led to the execution of many of the defendants. The trials are generally seen as part of Stalin's Great Purge, a campaign to rid the party of current or prior opposition, including Trotskyists and leading Bolshevik cadre members from the time of the Russian Revolution or earlier, who might even potentially become a figurehead for the growing discontent in the Soviet populace resulting from Stalin's mismanagement of the economy.: xvii  Stalin's rapid industrialization during the period of the First Five Year Plan and the brutality of the forced agricultural collectivization had led to an acute economic and political crisis in 1928–1933, made worse by the global Great Depression, which led to enormous suffering on the part of the Soviet workers and peasants. Stalin was acutely conscious of this fact and took steps to prevent it taking the form of an opposition inside the Communist Party of the Soviet Union to his increasingly totalitarian rule.: xvii