The New Zealand physicist Ernest Rutherford was an incubator of genius, and a genius himself. His position on this list is probably a little unorthodox as he wasn’t a very flashy scientist and he wasn’t a theoretical wizard. He just happened to be a surpassingly great physicist anyway.
When Rutherford started his work in the late 1800s, modern physics was still quite new. Classical mechanics had been fleshed out reasonably well, but relativity and quantum mechanics didn’t exist, and the world of the microscopic was very poorly understood. The very concept that there were such a thing as atoms wasn’t entirely without controversy. The structure of atoms was something not far removed from blind conjecture.
The first steps toward understanding came from the discovery and subsequent study of radioactivity. These little bits of atoms provided the clues which helped to push back the darkness of the interior of the atom. Rutherford was at the forefront of this effort, describing and naming alpha and beta radiation, andmaking the discovery of radioactive half-life.
Rutherford is best known for his direction and supervision of the Geiger-Marsden experiment, which is certainly one of the most beautiful experiments in physics. He fired alpha particles at gold atoms and by their scattering was able to determine that the mass of the atom was overwhelmingly concentrated in a tiny central nucleus. It’s both amazing for its elegance and the fact that it presaged quantum mechanics in an unexpected way. Classically, the behavior of particles scattering off of other particles is governed by a wholly different set of rules than it is in quantum mechanics. The classical rules for scattering are totally wrong at the subatomic level. But in an amazing coincidence, the quantum rules and classical rules happen to give the same answer for coulomb scattering off a nucleus. If it hadn’t, Rutherford’s experiment might well have been misinterpreted and subatomic physics would have probably been set back by years.
He hypothesized the existence of the neutron, and ran the institute where the neutron was discovered and the atom was first split. He was the first man in history to successfully perform alchemy. Well, nuclear transmutation of one element to another anyway.
So many things we take for granted as common and easy knowledge were first brought to light by Rutherford and his group. It’s hard to contribute more to physics than that.
Honorable Mention: Niels Bohr, for similar reasons.