Albert Einstein (March 14, 1879 – April 18, 1955) was a theoretical physicist who is widely regarded as one of the most influential scientists of all time. His many contributions to physics include the special and general theories of relativity, the founding of relativistic cosmology, the photon theory and wave-particle duality, and the quantum theory of atomic motion in solids. Einstein is best known for his theories of special relativity and general relativity. He received the 1921 Nobel Prize in Physics. He is often regarded as the father of modern physics.