Leó Szilárd
Leó Szilárd (1898–1964) was a Jewish Hungarian physicist who conceived the nuclear chain reaction in 1933, patented the idea of a nuclear reactor with Enrico Fermi, and in late 1939 wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb. Szilárd left Hungary because of the rising antisemitism under the Horthy regime, which excluded Jewish students from Hungary's universities.