The famous scientist who developed the theory of relativity is Albert Einstein. He introduced the special theory of relativity in 1905 and the general theory of relativity in 1915. His work revolutionized our understanding of space, time, and gravity, indicating that time and space are not absolute but are interwoven and relative to the observer's speed. Einstein's theories challenged conventional physics and laid the groundwork for modern theoretical physics. He is often regarded as one of the most influential scientists of the 20th century.