Einstein won the Nobel Prize for Physics in 1921 for his work on the photoelectric effect. He was awarded it for his work on the photo-electric effect, which is a manifestation of the quantum nature of light. General relativity is a theory of the behavior of space and time. Einstein's General Theory of Relativity was an entirely new theory of gravity, replacing the centuries-old theories of Isaac Newton.
Henri Poincaré and Hendrik Lorentz had pieces of the theory of special relativity, but Einstein was the first to assemble the whole theory together as an universal law