On this date in the year 534 B.C.E., Thespis reportedly became the first Western actor to portray a character onstage. Details are sketchy, but Aristotle wrote that Thespis, a Greek poet from Icaria, donned a mask and took on the persona of Dionysus, god of fertility, wine, and the theater. Up to this point, Greek theater mostly consisted of choruses singing songs about Greek myths. Thespis was the first one to actually pretend to be someone else, speaking dialogue from the point of view of that character.

-Writer’s Almanac for November 23, 2015

It is implied that Thespis invented acting in the Western world, and that prior to his performances, no one had ever assumed the resemblance of another person for the purpose of storytelling. In fact, Thespis is the first known actor in written plays. He may thus have had a substantial role in changing the way stories were told and inventing theatre as we know it today. In reverence to Thespis, actors in the English-speaking part of the world have been referred to as thespians.

-https://en.wikipedia.org/wiki/Thespis