Albert Einstein significantly contributed to the field of physics, particularly in theoretical physics. He is best known for his theories of relativity, including the special theory of relativity and the general theory of relativity. His groundbreaking work on the nature of light, energy, and the relationship between mass and energy (expressed in the famous equation E=mc²) revolutionized our understanding of space, time, and gravity. Einstein's contributions laid the foundation for many modern advancements in physics and changed how we perceive the universe.