Le籀 Szil獺rd (February 11, 1898 - May 30, 1964) was a Hungarian-American physicist and inventor. He 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. He hoped America would not use nuclear weapons, but that the threat of such weapons would force Germany and Japan to surrender. He worried about the long term implications of the usage of nuclear weapons, predicting that their usage by America would start a nuclear arms race with Russia. He drafted the Szil獺rd petition advocating demonstration of the atomic bomb. The Interim Committee instead chose to use atomic bombs against cities over the protests of Szil獺rd and other scientists. In 1947, he shifted his field of study from nuclear physics to biophysics and molecular biology, working extensively with Aaron Novick. The change is widely credited as Szil獺rd's zero interest to support the development of stronger nuclear weapons. In 1960, he was diagnosed with bladder cancer. In 1964, he died in his sleep of a heart attack at the age of 66.