Albert Einstein (March 14, 1879 - April 18, 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Best known for developing the theory of relativity, he also made important contributions to the development of the theory of quantum mechanics. Relativity and quantum mechanics are the two pillars of modern physics. His mass–energy equivalence formula E = mc2, which arises from relativity theory, has been dubbed "the world's most famous equation."