Russian actor, director, and teacher who represented in his work and teaching the precepts of Konstantin Stanislavsky.

Leonidov studied at the Moscow Imperial Theatrical School and worked as an actor in Kiev, Odessa, and at Moscow's Korsh Theatre before joining the Moscow Art Theatre in 1903 to work under Stanislavsky (Stanislavsky, Konstantin Sergeyevich). He made his debut there playing Pepel in Maksim Gorky's The Lower Depths, and, although he received favourable notice in a few comedy roles (Borkin in Anton Chekhov's Ivanov and Skalozub in Aleksandr S. Griboyedov's Woe from Wit), he went on to receive greater acclaim for his dramatic performances. His most brilliant performance was as Dmitry Karamazov in The Brothers Karamazov (1910). Among his outstanding roles were Cassio in Julius Caesar (1903) and the title roles in Peer Gynt (1912) and Othello (1930).

Leonidov's motion-picture career, begun in 1919, also emphasized his dramatic talents; his Ivan the Terrible in The Wings of a Serf (1926) and his portrayal of the title role in Gobsek (1935) are especially noteworthy. Leonidov was particularly adroit in conveying the theories and practice of his director, Stanislavsky, to theatre neophytes. He began teaching at the State Institute of Theatre Arts in 1935 and was its dean and artistic director from 1939 until his death.

He was also active as a theatre director; among his credits were stagings of Nikolay Y. Virta's Earth in 1937 and Gorky's Dostigaev and the Others in 1938. He was honoured as a People's Artist of the U.S.S.R. in 1936 and was the recipient of an Order of Lenin and an Order of the Red Banner of Labour.