Einstein is overrated for various reasons. It is not so well known that nearly all of the special theory of relativity had been published first by Henri Poincaré Hendrik Lorentz. It is known that Einstein had read some of it. We don't know how much because Einstein failed to cite his sources. Einstein got his final general relativity field equations from correspondence with David Hilbert. You can find details here, here, and here.
I am not trying to put Einstein down, but I think that there were a lot of others who contributed more.
I have seen Einstein quoted as saying, "The secret to creativity is knowing how to hide your sources." It appears that Einstein was one of the most notorious abusers of that secret in history.
Someone sent me this excerpt from the Feynman Lectures on Physics Vol. 1:
15.3 Equations (15.3) are known as a Lorentz transformation. Einstein, following a suggesin origionally made by Poincaré, then proposed that all physical laws should be of such a kind that they remain unchanged under a Lorwntz transformation.This book is one of the most respected Physics textbooks that has ever been written. So what I am saying here is certainly no secret. Lorentz and Poincare were two of the most distinguished scholars of the day, and they published openly in widely-read books and journals.
16.1 Poincaré made the following statement of the principle of relativity: "According to the principle of relativity, the laws of physical phenomena must be the same for a fixed observer as for an observer who has a uniform motion of translation relative to him, so that we have not, nor can we possible have, any means of discerning whether or not we are carried along in such a motion."
I conclude that it is wrong to call Special Relativity Einstein's theory. His contributions appear to be much less than those of Lorentz and Poincare. At best, it should be called the Lorentz-Poincare-Einstein theory of relativity. General Relativity should probably be called the Einstein-Hilbert theory.
I have heard various explanation for why Einstein did not get a Nobel Prize for relativity, but never the most straightforward one -- that Einstein did not create the theory and everyone at the time knew it.