Albert Einstein is credited with developing the theory of relativity, which fundamentally changed our understanding of physics. Published in two parts—special relativity in 1905 and general relativity in 1915—these theories introduced groundbreaking concepts. Special relativity established the idea that space and time are interwoven and relative to the observer’s speed. General relativity expanded this notion, describing gravity not as a force but as the curvature of spacetime caused by mass. Einstein's work has profoundly impacted modern physics and has been essential in fields ranging from cosmology to quantum mechanics.