Albert Einstein was a theoretical physicist who developed the general theory of relativity, one of the two pillars of modern physics. His famous equation, $E=mc^2$, established the equivalence of mass and energy, fundamentally changing how we understand the universe's mechanics. In 1921, he received the Nobel Prize in Physics, not for relativity (which was still controversial), but for his explanation of the photoelectric effect, which was pivotal in the development of quantum theory. A lifelong pacifist and humanist, Einstein fled Nazi Germany in 1933 and settled in the United States. While his work laid the theoretical foundation for the atomic bomb, he later became a vocal advocate for nuclear disarmament and world peace. His name has become synonymous with 'genius,' and his theories continue to be proven correct by modern technology, including the GPS systems in our smartphones, which must account for relativistic time dilation to remain accurate.