Thespis (; Greek: Θέσπις; fl. 6th century BC) was an Ancient Greek poet. He was born in the ancient city of Icarius (present-day Dionysos, Greece). According to certain Ancient Greek sources and especially Aristotle, he was the first person ever to appear on stage as an actor playing a character in a play (instead of speaking as themselves). In other sources, he is said to have introduced the first principal actor in addition to the chorus. He is often called the "Inventor of Tragedy".

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.

This new style was called tragedy, and Thespis was the most popular exponent of it. Eventually, in 534 BC competitions to find the best tragedy were instituted at the City Dionysia in Athens, and Thespis won the first documented competition. Capitalising on his success, Thespis also invented theatrical touring; he would tour various cities while carrying his costumes, masks and other props in a horse-drawn wagon.