In 1905 while working at the Swiss Patent Office Einstein devoped the Theory of Special Relavity - that same year he submitted his PhD Dissertation to the University of Zurn. By 1905 Einstein was well known as that year he published 4 papers - each being part of modern physics.
From the special theory of relativity the famous equation E=mc2 (squared) which was the foundation of the Atomic bomb.
M is the mass and c = the speed of light squared - so that a small mass contains a great deal of energy.
Interesting is that Einstein didn't believe in Quantum Mechanics. That is where his famous quote came from - God doesn't play dice....
Actually, Quantum Mechanics were far more mysterious at the time.
I have read a great deal about Einstein, Wigner, John Wheeler, Fermi, Feynman... mostly during college.
IG