J. Robert Oppenheimer: Oppenheimer was the director of the Los Alamos Laboratory where under the manhattan project, the atomic bomb was developed and tested.
Albert Einstein: Einstein was a German Physicist and semi-pacifist who collaborated with the allies early on in the war, urging them to research the possibility of a uranium fission bomb before the Nazis were able to do so. His research into the atomic bomb was indirect, but he did sign letters to FDR to convince him of the need to discover the nuclear fission before the Nazi's did.
Richard Feynman: Feynman was an American Physicist and the leader of the theortical division of the Manhattan project as well as the computing portion of the project. He was a direct witness of the first test blast of the atomic weapons.
Edward Teller: Teller was another scientist who worked on the Manhattan project developing the atomic bomb, as well as one fo the leaders of the later research into developing a more powerful nuclear weapon, the hydrogen fusion bomb.
Phillip Morrison: Morrison was an American physicist and one of the youngest workers on the Manhattan Project. He worked early on in the refinement of uranium and plutonium for the bomb with Physicist Enrico Fermi, then latter worked directly in construction of the bomb's core in Los Alamos.