Who discovered dual nature of light?

Max Planck discovered that, if one assumes that light was composed of "chunks" (he used the Word "quanta"), and that each chunk of light had an energy equal to its frequency times a constant (which eventually became known as "Planck Constant"); the spectrum of blackbody radiation could be easily explained. Planck, however, did not think that these quanta were real, he only noted this fact as a mathematical curiOSity.

Einstein noted that making the exact same assumption would fully explain the photo-electric effect. He also made the intellectual leap of stating these quanta were real particles, and not just mathematical models.

These "quanta" of light eventually became known as photons.