Chaim Azriel Weizmann (Hebrew: חיים עזריאל ויצמן Chayyim Azri'el Vaytsman, Russian: Хаим Евзорович Вейцман, Khaim Evzorovich Veytsman; 27 November 1874 – 9 November 1952) was a Russian-born biochemist, Zionist leader and Israeli statesman who served as president of the Zionist Organization and later as the first president of Israel. He was elected on 16 February 1949, and served until his death in 1952. Weizmann was fundamental in obtaining the Balfour Declaration and later convincing the United States government to recognize the newly formed State of Israel.

As a biochemist, Weizmann is considered to be the 'father' of industrial fermentation. He developed the acetone–butanol–ethanol fermentation process, which produces acetone, n-butanol and ethanol through bacterial fermentation. His acetone production method was of great importance in the manufacture of cordite explosive propellants for the British war industry during World War I. He founded the Sieff Research Institute in Rehovot (later renamed the Weizmann Institute of Science in his honor), and was instrumental in the establishment of the Hebrew University of Jerusalem.