Sir Isaac Newton:
Discovered gravity while watching an apple fall from a tree and wondering why the moon did not fall. He invented Calculus to make the calculations he needed for Physics measurements. Claimed to have invented Physics as well.
Nobel Prize winner for the Photoelectric Effect. Most famous for the theory of relativity. The theory of relativity was proven correct in 1971, 16 years after Dr. Einstein's Death
Dr. Richard Feynman
Won the Nobel Prize in Physics for Quantum Electrodynamics: how electrons spin. He was well known as a scientist who made hard concepts easy for non-scientists to understand. He worked on the Manhattan Project and was the scientist who figured out what made the space shuttle Challenger explode.
Dr. Stephen Hawking:
Dr. Hawking would probably not be famous if he had not been stricken with A.L.S. in his 20's. Since then, while confined to a wheel chair, he has become one of our greatest thinkers. The X-ray radiation ejected from a black hole has been named after him.