Karl Schwarzschild published the 1916 solution describing spacetime around a nonrotating spherical mass.
Schwarzschild derived the solution shortly after Einstein presented general relativity in 1915. He was serving on the Eastern Front during the First World War when he sent Einstein the result. The solution became the first exact solution to Einstein’s field equations outside a spherically symmetric, nonrotating, uncharged body.
The metric introduced the characteristic length now called the Schwarzschild radius. In modern interpretation, if a mass is compressed within that radius, the solution contains an event horizon. At the time, the physical meaning of such an object was not yet fully understood, and black holes were not immediately accepted as astrophysical realities.
Schwarzschild’s work is often confused with later contributions. Roy Kerr found the solution for rotating black holes in 1963, while Einstein supplied the underlying theory. Schwarzschild also made important contributions to stellar structure and observational astronomy.