Actually, no - Einstein won the 1921 Nobel Prize in Physics for his explanation of the photoelectric effect, not for his theory of relativity. The Nobel Committee specifically cited his work on theoretical physics and "especially for his discovery of the law of the photoelectric effect."

This might seem surprising given how famous relativity is today, but at the time, relativity was still considered quite controversial and hadn't yet received the experimental confirmation it has now. The photoelectric effect work was seen as more definitively established and was foundational to quantum theory.

It's one of those interesting historical details where what someone is most famous for isn't necessarily what they won their major awards for!
