Albert Einstein was a theoretical physicist whose genius fundamentally altered our understanding of space, time, and gravity. In his 'Annus Mirabilis' (miracle year) of 1905, he published four papers that introduced Special Relativity and the equation $E = mc^2$, proving that mass and energy are interchangeable. He later developed General Relativity, which describes gravity not as a force, but as a curvature of spacetime caused by mass. Einstein’s work led to the development of nuclear energy and explained the photoelectric effect (for which he won the Nobel Prize). His name has become globally synonymous with the word 'genius,' and his theories remain the foundation of modern cosmology.