Who invented the first Atomic Bomb?

A very large number of scientists and engineers working together in the Manhattan Project. There's no one person that can be definitively pointed to as the "inventor" of the atomic bomb; the list of people who were involved reads like a Who's Who in Physics of the first half of the 20th century: Oppenheimer, Bohr, Fermi, Seaborg, Feynman, Szilard, and literally hundreds of others.