Actually, Einstein won the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect, not for relativity. The Nobel Committee was cautious about relativity at the time, as it was still considered somewhat controversial. His work on the photoelectric effect, which showed that light behaves as particles (photons) in certain situations, was more experimentally verified and less disputed. This work was crucial for the development of quantum mechanics.

It's a common misconception that he won it for relativity, probably because his theories of special and general relativity are what he's most famous for today.
