Einstein with his cousin and second wife Elsa Einstein Lowenthal, Caputh, Germany, circa 1930. Albert Einstein (March 14, 1879 - April 18, 1955) was a German-born theoretical physicist. He developed the general theory of relativity, one of the two pillars of modern physics. He is best known in popular culture for his mass-energy equivalence formula E = mc2. He received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect". He was visiting the US when Hitler came to power in 1933, and did not go back to Germany. He settled in America becoming a citizen in 1940. He helped alert President Roosevelt that Germany might be developing an atomic weapon, and recommended that the US begin similar research. He was in support of defending the Allied forces, but largely denounced using the discovery of nuclear fission as a weapon. Later, together with Bertrand Russell, Einstein signed the Russell-Einstein Manifesto, which highlighted the danger of nuclear weapons. Einstein was affiliated with the Institute for Advanced Study in Princeton until his death in 1955, at the age of 76. His great intelligence and originality have made the word Einstein synonymous with genius.