Leó Szilárd (Hungarian: Szilárd Leó, February 11, 1898 – May 30, 1964) was a 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, and the atomic bomb.
He was born in Budapest in the Austro-Hungarian Empire, and died in La Jolla, California.
"Because of the danger that Hitler might be the first to have the bomb, I signed a letter to the President which had been drafted by Szilard. Had I known that the fear was not justified, I would not have participated in opening this Pandora's box, nor would Szilard. For my distrust of governments was not limited to Germany." The photograph shows a postwar reconstruction of the signing.