Alexander Alexandrovich Blok (Russian: Алекса́ндр Алекса́ндрович Бло́к, IPA: [ɐlʲɪˈksandr ɐlʲɪˈksandrəvʲɪtɕ ˈblok] ^ⓘ; 28 November [O.S. 16 November] 1880 – 7 August 1921) was the most well-known Russian lyrical poet during the Silver Age of Russian Poetry.

Blok was born in Saint Petersburg, into an intellectual family of Alexander Lvovich Blok and Alexandra Andreevna Beketova. His father was a law professor in Warsaw, and his maternal grandfather, Andrey Beketov, was a famous botanist and the rector of Saint Petersburg State University. After his parents' separation, Blok lived with aristocratic relatives at the manor Shakhmatovo near Moscow, where he discovered the philosophy of Vladimir Solovyov, and the verse of then-obscure 19th-century poets, Fyodor Tyutchev and Afanasy Fet. These influences would affect his early publications, later collected in the book Ante Lucem.

In 1903 he married the actress Lyubov (Lyuba) Dmitrievna Mendeleeva, daughter of the renowned chemist Dmitri Mendeleev. Later, she would involve him in a complicated love-hate relationship with his fellow Symbolist Andrei Bely. To Lyuba he dedicated a cycle of poetry that made him famous, Stikhi o Prekrasnoi Dame (Verses About the Beautiful Lady, 1904).

Blok enthusiastically greeted the 1905 Russian Revolution. During the last period of his life, Blok emphasised political themes, pondering the messianic destiny of his country (Vozmezdie, 1910–21; Rodina, 1907–16; Skify, 1918). In 1906 he wrote an encomium to Mikhail Bakunin. Influenced by Solovyov's doctrines, he had vague apocalyptic apprehensions and often vacillated between hope and despair. "I feel that a great event was coming, but what it was exactly was not revealed to me", he wrote in his diary during the summer of 1917. Quite unexpectedly for most of his admirers, he accepted the October Revolution as the final resolution of these apocalyptic yearnings.

In May 1917 Blok was appointed as a stenographer for the Extraordinary Commission to investigate illegal actions ex officio Ministers or to transcribe the (Thirteenth Section's) interrogations of those who knew Grigori Rasputin. According to Orlando Figes he was only present at the interrogation.

In November 1917, a few days after the October Revolution, the People's Commissar of Education, Anatoly Lunacharsky invited 120 of the leading writers and other cultural figures to a meeting, which almost all boycotted. Blok was one of five to attend, along with Vladimir Mayakovsky, Vsevolod Meyerhold and two others. When the Socialist Academy of Social Sciences was established in 1918, Blok became a participant.

His poem, The Twelve, written in 1918, describes 12 Red Guards in the violent chaos of the Russian Civil War, who are likened to the Apostles, while "Ahead of them, Jesus Christ goes."

Because this early show of support, Blok continued to be honoured by the Bolsheviks, despite his pre-revolutionary religious imagery, and his later disillusionment. In 1923, Leon Trotsky devoted a whole chapter of his book Literature and Revolution to Blok, saying that "Blok belonged to pre-October literature, but he overcame this, and entered into the sphere of October when he wrote The Twelve. That is why he will occupy a special place in the history of Russian literature." Given the official report on poetry to the First Congress of Soviet Writers , Nikolai Bukharin praised Blok as "a poet of tremendous power (whose) verse achieves a chiselled monumentality..." but added that "he thought that with the sign of the Cross he could bless and at the same time exorcise the image of the unfolding revolution, and he perished without having spoke his final word."