The scientist known for the theory of relativity is Albert Einstein. He introduced the special theory of relativity in 1905 and the general theory of relativity in 1915. The special theory revolutionized our understanding of space and time, proposing that the laws of physics are the same in all inertial frames of reference and that the speed of light is constant regardless of the observer's motion. The general theory of relativity further expanded this concept by describing gravity not as a force but as a curvature of spacetime caused by mass. Einstein's theories fundamentally changed physics, influencing a wide range of scientific fields.