We take drama so much for granted nowdays. The idea is not a "natural" one. It had to be invented. The inventor, according to tradition was an Athenian named THESPIS.

AESCHYLUS, in the next generation transforms the invention of Thespis by adding a second actor to the cast of chorus. Tragedy had a history in Athens of about two hundred years, and the rules were little alterered other than the addition of a third actor.