Albert Einstein (German: IPA: [ˈalbɐt ˈaɪ̯nʃtaɪ̯n] (Auio file) (help·info); English: IPA: /ˈælbɝt ˈaɪnstaɪn/) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist. He is best known for his theory of relativity and specifically mass–energy equivalence, E = mc2. Einstein 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."