Mstislav Vsevolodovich Keldysh (Russian: Мстисла́в Все́володович Ке́лдыш; 10 February [O.S. 28 January] 1911 – 24 June 1978) was a Soviet mathematician who worked as an engineer in the Soviet space program.
He was the academician of the Academy of Sciences of the Soviet Union (1946), President of the Academy of Sciences of the Soviet Union (1961–1975), three-time Hero of Socialist Labour (1956, 1961, 1971), and fellow of the Royal Society of Edinburgh (1968). He was one of the key figures behind the Soviet space program. Among scientific circles of the USSR Keldysh was known by the epithet "the Chief Theoretician" in analogy with epithet "the Chief Designer" used for Sergei Korolev.
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