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.