Sergei Gustavovich Legat (Russian: Серге́й Густа́вович Лега́т; 27 September 1875 – 1 November 1905) was a Russian ballet dancer. He was born in Moscow and died in Saint Petersburg.

The younger brother of Nikolai Legat, he studied at the imperial ballet school with Pavel Gerdt, Christian Johansson, Lev Ivanov and his brother. Legat joined the Mariinsky Theatre in 1894 and quickly became a soloist. Admired for his stylistic performances he also taught, with pupils including Vaslav Nijinsky. He originated the dual role of the Nutcracker/Prince in Tchaikovsky's famous ballet. He married Marie Petipa (1857–1930). At the outbreak of the First Russian Revolution he fell out with the authorities and committed suicide, slashing his throat with a razor.

Many of the male variations that make up the traditional classical ballet repertory were created especially for him at the turn of the 20th century.