Albert Einstein was a German-born theoretical physicist who developed the theory of relativity, one of the pillars of modern physics. He is best known for his mass–energy equivalence formula E=mc2. Einstein received numerous honors including the Nobel Prize in Physics in 1921 for his services to theoretical physics and especially for his discovery of the law of the photoelectric effect. He made several important contributions to physics including his work on Brownian motion, quantum theory of light, special theory of relativity, and the link between mass and energy.