Well you have the guy who found uranium, the guy who ran electrical checks through a vacuum, the guy who found pitchblende, and then Marie Curie who did the experiments with refined pitchblende to create X-ray machines.

If you want to talk specifically about nuclear energy and weapons then you’re probably looking for Rutherford. But he wouldn’t even be conducting those experiments without Curie, Röntgen, and Becquerel.