Which scientist developed the theory of general relativity?

Albert Einstein published general relativity in 1915, a decade after his special theory of relativity. Special relativity dealt with observers moving at constant speed and showed that time and length depend on motion. General relativity extended the idea to acceleration and gravity, and its central move was to stop treating gravity as a force at all. Instead, mass and energy curve the fabric of spacetime, and objects moving through that curvature follow paths that look like orbits or falling. The theory made testable predictions Newton's could not: it explained a small anomaly in Mercury's orbit that had puzzled astronomers, and it forecast that starlight passing close to the Sun would be deflected, confirmed during a solar eclipse in 1919. It also predicted that clocks run slower in stronger gravity, an effect real enough that satellite navigation systems must correct for it, and that violent events send ripples of gravitational waves through space.

Black holes emerged as a solution to Einstein's field equations before anyone expected to find one in the sky.