Who came up with the theory of plate tectonics?

Alfred Wagner called his theory Continental Drift, but Plate tectonics is his theory reworked and improved.

Wagner's theory was rejected because it violated the principle of uniformtarism, the current timeline of geological fossil formation, had no explanation of a force that could move the vast continents, and contradicted the geosyncline theory of mountain formation.

Scientific discoveries of the mid Atlantic ridges and sea floor spreading, mirrored magnetic reversals, subduction zones and the related volcanic zones made rejection of Alfred Wagner's theory difficult. The idea of convection currents was added to Wagner's theory to provide a mechanism for the movement of the continents.
The timeline of geological recorded was revised to correspond to the evidence of continental spreading. Instead of the rapid movement of the continents proposed by Wagner, the movement was proposed to be very slow over vast times to agree with the theory of uniformtarism.

The revised theory of Plate Tectonics proved to be a better explanation of the location and causes of earthquakes and volcanos.

The theory explained the mid Atlantic Ridges and mountain building.
Even so the evolutionary scientists like Gaylord Simpson opposed the theory through the 1970s.

Alfred Wagner with his theory of Continental Drift was the precursor of the modern Plate Tectonic Theory.