Whose theory predicted black holes?

Albert Einstein's general relativity created the framework in which black holes became possible. Although Einstein himself was skeptical of the idea, later solutions to his equations showed that sufficiently massive and compact objects could collapse into regions from which not even light can escape. The concept was developed further by physicists such as Karl Schwarzschild, John Wheeler and others. Black holes are now observed indirectly through stars, X-ray emissions and gravitational waves.