It's tricky to name "fathers of the bomb" because it isn't clear what that means. It has an arbitrary feel. Is Lise Meitner the "mother of the bomb" because of her work on fission theory? Is Enrico Fermi arguably more important than Oppenheimer, for his work on slow neutrons and chain reacting systems? Do we gauge this with a game of "who can we remove in history and make the most difference?" — if so, then General Leslie Groves is the true "father of the atomic bomb," for his presence was arguably the most important of all of theirs, much more so than Oppenheimer's.

The Manhattan Project involved the labor of some half-a-million people. That's nearly 1% of the entire US civilian labor force during World War II. Most of them did not know what they were building. If we constrain it to scientists, at Los Alamos there were several thousand, and there were another several thousand spread among other important lab sites, including UC Berkeley, University of Chicago, Oak Ridge, Hanford, and dozens of smaller sites (MIT, University of Virginia, Princeton, University of Toronto, UC Davis, Iowa State University, and many, many more).

Identifying individual "fathers" (aside from the gender issues — there were at least 20 women scientists and 50 women technicians at Los Alamos) is probably not the best way to think about the project. The atomic bomb was an immense undertaking on a scale that can be hard to fathom. Trying to identify one or two individuals can be a way to make the history more personal, but it runs the risk of thinking that this work was about individuals, rather than about the massive collective undertaking. This is why, if anyone, I would put Groves at the top of the list — he's the one that really launched the collective effort and worked to keep it running. He didn't come up with equations or designs or concepts, but he did make sure the infrastructure was there so that all of those things, and many more, were accomplished.

Edward Teller was an important figure, having contributed to the pit implosion design of the Trinity test and Fat Man (Nagasaki) bombs. Perhaps more notably, he had a fascination with fusion weapons even during the Manhattan Project and continued pushing for even more destructive weaponry, leading to the hydrogen bomb and the US-Soviet arms race that hung global consequences over the Cold War.