Answer:
Signed by Albert Einstein but written by Leó Szilard in consultation with physicists Edward Teller and Eugene Paul Wigner.
The letter was signed by Einstein on August 2, and given to Roosevelt by economist Alexander Sachs. It warned Roosevelt that Nazi Germany might be conducting research into the use of nuclear fusion to create atomic bombs and suggested that the United States should initiate its own research on the subject.
However, it did not come into his hands until October 11 due to the president's concern with the German invasion of Poland, which would start World War II. After hearing Sachs' summary of the letter, Roosevelt authorized the establishment of the Uranium Advisory Committee. Shortly thereafter, the first funds were provided for neutron experiments, conducted by Enrico Fermi at the University of Chicago.