Sergei Yakovlevich Efron (
Russian: Серге́й Я́ковлевич Эфро́н; 8 October 1893 – 16 October 1941), nicknamed Seryozha, was a Russian poet, officer of
White Army and husband of
Marina Tsvetaeva. While in emigration, he was recruited by the Soviet
NKVD. After returning to USSR from France, he was executed.