Boris Nikolaevich Bugaev (Russian: Бори́с Никола́евич Буга́ев, IPA: [bɐˈrʲis nʲɪkɐˈlajɪvʲɪdʑ bʊˈɡajɪf] ^ⓘ; 26 October [O.S. 14 October] 1880 – 8 January 1934), better known by the pen name Andrei Bely or Biely, was a Russian and Soviet novelist, Symbolist poet, theorist and literary critic. He was a committed anthroposophist and follower of Rudolf Steiner. His novel Petersburg (1913/1922) was regarded by Vladimir Nabokov as the third-greatest masterpiece of modernist literature. The Andrei Bely Prize (Премия Андрея Белого), one of the most important prizes in Russian literature, was named after him. His poems were set to music and performed by Russian singer-songwriters.

Boris Bugaev was born in Moscow, into a prominent intellectual family. His father, Nikolai Bugaev, was a noted mathematician who is regarded as a founder of the Moscow school of mathematics. His mother, Aleksandra Dmitrievna (née Egorova), was not only highly intelligent but a famous society beauty, and the focus of considerable gossip. She was also a pianist, providing Bugaev his musical education at a young age.

Young Boris grew up at the Arbat, a historical area in Moscow. He was a polymath whose interests included mathematics, biology, chemistry, music, philosophy, and literature. Bugaev attended university at the University of Moscow. He would go on to take part in both the Symbolist movement and the Russian school of neo-Kantianism. Bugaev became friendly with Alexander Blok and his wife; he fell in love with her, which caused tensions between the two poets. Bugaev was invited but was unable to attend their wedding due to his father's death.

Nikolai Bugaev was well known for his influential philosophical essays, in which he decried geometry and probability and trumpeted the virtues of hard analysis. Despite—or because of—his father's mathematical tastes, Boris Bugaev was fascinated by probability and particularly by entropy, a notion to which he frequently refers in works such as Kotik Letaev.

As a young man, Bely was strongly influenced by his acquaintance with the family of philosopher Vladimir Solovyov, especially Vladimir's younger brother Mikhail, described in his long autobiographical poem The First Encounter (1921); the title is a reflection of Vladimir Solovyov's Three Encounters. It was Mikhail Solovyov who gave Bugaev his pseudonym Andrei Bely.^{[citation needed]}

In his later years Bely was influenced by Rudolf Steiner's anthroposophy and became a personal friend of Steiner's. His ideas covering this philosophy included his attempts to connect Vladimir Solovyov's philosophical ideas with Steiner's Spiritual Science. One of his notions was the Eternal Feminine, which he equated it with the "world soul" and the "supra-individual ego", the ego shared by all individuals. He spent time between Switzerland, Germany, and Russia, during its revolution. He supported the Bolshevik rise to power and later dedicated his efforts to Soviet culture, serving on the Organizational Committee of the Union of Soviet Writers. He died, aged 53, in Moscow. Several of the numerous poems written in Moscow in January 1934 were inspired by Bely's death.

Bely did not accomplish his reformation of Russian prose single‐handedly: other major Symbolist novelists, especially Fyodor Sologub and Alexei Remizov, also had a hand in it. It is to Bely's influence, however, more than anyone else's, that we can trace the literary origins of some of the finest early Soviet writers, such as Zamyatin, Pilnyak, Babel and Andrei Platonov ... Moreover, Bely's novels prefigure and map out both the sensibility and the structural devices of the later Western novel with such thoroughness that a person familiar with his work who reads Joyce's Ulysses or Robbe‐Grillet's Jealousy or even Thomas Pynchon's Gravity's Rainbow for the first time can't shake off the feeling that their authors somehow must have known Bely, even though there's not a chance that they did.

— Simon Karlinsky, The New York Times, 1974