Sergei Pavlovich Diaghilev (Сергей Павлович Дягилев) (March 19, 1872 – August 19, 1929), often known as Serge, was a Russian ballet impresario and founder of the Ballets Russes from which many famous dancers and choreographers would later arise.

Born in Perm, Russia to an aristocratic family, he studied law in university. He also engaged in painting, singing and music.

In 1905 he mounted in St Petersburg an exhibition of Russian portrait painting, and in the following year took a major exhibition of Russian art to the Petit Palais in Paris. It was the beginning of a long involvement with France. In 1907 he presented five concerts of Russian music in Paris, and in 1908 mounted a production of Boris Godunov, starring Fyodor Chaliapin, at the Paris Opera.

This led to an invitation to return the following year with ballet as well as opera, and thus to the launching of his famous Ballets Russes. The company included the best young Russian dancers, among them Anna Pavlova and Vaslav Nijinsky, and their first night on 19 May 1909 was a sensation.

Diaghilev commissioned ballet music from composers such as Claude Debussy (Jeux, 1913), Maurice Ravel (Daphnis et Chlo�, 1912), Erik Satie (Parade, 1917), Richard Strauss (Josephs-Legende, 1914), Sergei Prokofiev (Ala and Lolly, rejected by Diaghilev and turned into the Scythian Suite, and Chout, 1915), Ottorino Respighi (La Boutique Fantasque, 1918), Francis Poulenc (Les Biches, 1923) and others. His choreographer Mikhail Fokine often adapted the music for ballet. Dhiagilev also worked with dancer and ballet master Leonid Myasin.

The artistic director for the Ballets Russes was Leon Bakst, whose connection with Diaghilev extended back to 1898, when he, Diaghilev and Alexander Benois founded the avant-garde group 'World of Art' (Mir Iskusstva). Together they developed a more complicated form of ballet with show-elements intended to appeal to the general public, rather than solely the aristocracy. The exotic appeal of the Ballets Russes had an effect on Fauvist painters and the nascent Art Deco style.

Perhaps Diaghilev's most notable composer collaborator, however, was Igor Stravinsky. Diaghilev heard Stravinsky's early orchestral works Fireworks and Scherzo Fantastique, and was impressed enough to ask Stravinsky to arrange some pieces by Frederic Chopin for the Ballets Russes. In 1910, he commissioned his first score from Stravinsky, The Firebird. Petrushka (1911) and The Rite of Spring (1913) followed shortly afterwards, and the two also worked together on Pulcinella (1920) and Les Noces (1923).

Dhiagilev staged “The Sleeping Beauty” of Tchaikovsky in London in 1921; despite being well received by the public it was not a financial success. The later years of the Ballets Russes were often considered too "intellectual", too "stylish" and seldom had the unconditional success of the first few seasons.

The end of the 19th century brought a development in the handling of tonality, harmony, rhythm and meter towards more freedom. Until that time, rigid harmonic schemes had forced rhythmic patterns to stay fairly uncomplicated. Around the turn of the century, however, harmonic and metric devices became either more rigid, or much more unpredictable, and each approach had a liberating effect on rhythm, which also affected ballet. Diaghilev was a pioneer in adapting these new musical styles to modern ballet. When Ravel used a 5/4 time in the final part of his ballet Daphnis and Chlo� (1912), dancers of the Ballets Russes sang Ser-ge-dia-ghi-lev during rehearsals to keep the correct rhythm.

Members of Diaghilev's Ballets Russes later went on to found ballet traditions in the United States (George Balanchine) and England (Ninette de Valois and Marie Rambert). Ballet master Serge Lifar went on to revive the Paris Opera.

He died in Venice, Italy on August 19, 1929 and is buried on the nearby island of San Michele.