Albert Einstein was a theoretical physicist born in 1879 in Ulm, Germany. He is best known for developing the theory of relativity, which revolutionized our understanding of space, time, and gravity. His famous equation, E=mc², demonstrates the equivalence of mass and energy. In 1921, he received the Nobel Prize in Physics for his explanation of the photoelectric effect. Einstein's work profoundly impacted the development of quantum mechanics and modern physics.