Albert Einstein was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics. His work is also known for its influence on the philosophy of science. He is widely regarded as one of the most influential scientists of all time and a key figure in the development of modern physics. He received the 1921 Nobel Prize in Physics for his services to theoretical physics, especially his discovery of the law of the photoelectric effect, a pivotal step in the evolution of quantum theory.