Nikolai Ivanovich Bukharin (/buːˈxɑːrɪn/; Russian: Николай Иванович Бухарин, IPA: [nʲɪkɐˈlaj ɪˈvanəvʲɪdʑ bʊˈxarʲɪn]; 9 October [O.S. 27 September] 1888 – 15 March 1938) was a Russian revolutionary, Soviet politician, and Marxist theorist. A prominent Bolshevik described by Vladimir Lenin as a "most valuable and major theorist" of the Communist Party, Bukharin was active in the Soviet government from 1917 until his purge in 1937.

Bukharin joined the Russian Social Democratic Labour Party in 1906, and studied economics at Moscow Imperial University. In 1910, he was arrested and internally exiled to Onega, but the following year escaped abroad, where he met Lenin and Leon Trotsky and built his reputation with works such as Imperialism and World Economy (1915). After the February Revolution of 1917, Bukharin returned to Moscow and became a leading figure in the party, and after the October Revolution became editor of its newspaper, Pravda. He led the Left Communist faction in 1918, and during the civil war wrote The ABC of Communism (1920; with Yevgeni Preobrazhensky) and Historical Materialism: A System of Sociology (1921), among other works.

Bukharin was initially a proponent of war communism, but in 1921 supported the introduction of the New Economic Policy (NEP) and became its chief theorist and advocate, supporting the party leadership against Trotsky and the Left Opposition. By late 1924, this stance had positioned Bukharin favourably as Joseph Stalin's chief ally, with Bukharin soon elaborating Stalin's theory of "socialism in one country". From 1926 to 1929, Bukharin served as General Secretary of the Comintern's executive committee. Following Stalin's decision to proceed with agricultural collectivisation in the Great Break, Bukharin was labelled as the leader of the Right Opposition and was removed from Pravda, the Comintern, and the party leadership in 1929.

After a period in lower positions, in 1934 Bukharin was reelected to the Central Committee and became editor of the newspaper Izvestia. He was a principal architect of the 1936 Soviet Constitution. During the Great Purge, Bukharin was accused of treason in February 1937 and executed after a show trial in 1938.

Nikolai Bukharin was born on 27 September (9 October, new style), 1888, in Moscow. He was the second son of two schoolteachers, Ivan Gavrilovich Bukharin and Liubov Ivanovna Bukharina. According to Nikolai his father did not believe in God and, from the age of four, often asked him to recite poetry for family friends. His childhood is vividly recounted in his mostly autobiographic novel How It All Began.

Bukharin's political life began at the age of sixteen, with his lifelong friend Ilya Ehrenburg, when they participated in student activities at Moscow University related to the Russian Revolution of 1905. He joined the Russian Social Democratic Labour Party in 1906, and became a member of its Bolshevik faction. With Grigori Sokolnikov, Bukharin convened the 1907 national youth conference in Moscow, which was later considered the founding of Komsomol.

By age twenty, he was a member of the Moscow Committee of the party. The committee was widely infiltrated by the Tsarist secret police, the Okhrana. As one of its leaders, Bukharin quickly became a person of interest to them. During this time, he became closely associated with Valerian Obolensky and Vladimir Smirnov. He also met his future first wife, Nadezhda Mikhailovna Lukina, his cousin and the sister of Nikolai Lukin, who was also a member of the party. They married in 1911, soon after returning from internal exile.

In 1911, after a brief imprisonment, Bukharin was exiled to Onega in Arkhangelsk, but he soon escaped to Hanover. He stayed in Germany for a year before visiting Kraków (Poland) in 1912 to meet Vladimir Lenin for the first time. During the exile, he continued his education and wrote several books that established him in his 20s as a major Bolshevik theorist. His work Imperialism and World Economy influenced Lenin, who freely borrowed from it^{[citation needed]} in his larger and better-known work, Imperialism, the Highest Stage of Capitalism. He and Lenin also often had hot disputes on theoretical issues, as well as Bukharin's closeness with the European Left and his anti-statist tendencies. Bukharin developed an interest in the works of Austrian Marxists and heterodox Marxist economic theorists, such as Aleksandr Bogdanov, who did not agree with Lenin. Also, while in Vienna in 1913, he helped the Georgian Bolshevik Joseph Stalin write an article "Marxism and the National Question" at Lenin's request.^{[citation needed]}