Who was the first known actor in written plays?

Thespis of Icaria (present-day Dionysos, Greece), according to certain Ancient Greek sources and especially Aristotle, was the first person ever to appear on stage as an actor playing a character in a play (instead of speaking as him or herself).

Thespis was a singer of dithyrambs (songs about stories from mythology with choric refrains). He is credited with introducing a new style in which one singer or actor performed the words of individual characters in the stories, distinguishing between the characters with the aid of different masks.

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 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.