Leo Szilard was among the most influential scientists of his era. In 1898, he was born in Budapest, Hungary. He attended the city's technical university, but was drafted into the Austro-Hungarian Army before he could complete his studies. After the war, Admiral Horthy's repressive anti-Semitic regime took control of the country. Szilard, a Jew, left the country to continue his studies at the Berlin Institute of Technology. While at Berlin he studied under Albert Einstein, whom he would maintain a collaborative relationship with for many years to come.
Like his good friend and fellow Hungarian, Edward Teller, Szilard was eventually chased out of continental Europe because of his ethnicity. He fled Germany upon Hitler's assumption of power in 1933 and enjoyed a fellowship at Oxford University for the next five years. Szilard moved to New York in 1938, fearing the outbreak of war in Europe was imminent. When the Germans discovered fission, he drafted a letter of warning to President Roosevelt and asked his old teacher, Einstein, to sign it. Einstein agreed, thus setting in motion the development of the atomic bomb.
During the war, Szilard worked at Arthur Compton's metallurgical laboratory at the University of Chicago and acted as a consultant on Project Y. Though Szilard had called for the development of an atomic bomb to meet a potential German challenge, he felt that the bomb should not be used against the Japanese to end World War II. He felt so strongly on the issue, that he authored a petition to the president against the bomb's use. In part it read:
The seventy signatures Szilard collected included those of his fellow Hungarian Eugene P. Wigner and the physicist and author, Ralph E. Lapp. Just as Szilard had been the first to call for the development of the atomic bomb in America he, ironically, was the first to organize opposition against its use.
After the war, Szilard focused his energy on trying to control the power he was in large part responsible for unleashing. Along with Einstein and several other physicists, he established the Emergency Committee of Atomic Scientists in 1946. He left the field of physics altogether a few years later, opting for a career in molecular biology. In the early 1950s, he publicly opposed the development of the hydrogen bomb along with many other concerned scientists, but to no avail. A decade later, Szilard developed bladder cancer, and designed a successful radiation treatment regimen to combat it. In his final years, he founded the Council for a Livable World, which is still active today. Szilard died of a heart attack in May 1964.