The theory of relativity was discovered by Albert Einstein, a German-born physicist, in the early 20th century. The theory comprises two parts: special relativity, introduced in 1905, and general relativity, published in 1915. Special relativity revolutionized our understanding of space and time, proposing that the laws of physics are the same for all observers regardless of their relative motion and that the speed of light is constant in a vacuum. General relativity further expanded on these ideas, providing a new understanding of gravity as the curvature of spacetime caused by mass. Einstein's work has had profound implications across multiple scientific fields.