Originally, Greek theater was part of the Dionysian festival, a pressure-valve that released inhibitions and included songs, wine and goat sacrifices. Around 625 B.C. dithyrambs, or hymns, began to be included. Arion of Corinth called his hymnic creations "tragikon drama" and sang specifically, as himself, about the sacrificial goats. The tragedies of Greek theater thus began as testimonials to scapegoats, much like the Christ figures in modern literature.
Ninety years post-Arion, the chorister Thespis began his tragic festivals, where he would present the startling innovation of addressing the audience as a character other than himself. Eventually he added another actor, then another; this triad would present tragic pieces designed to calm over-enthused crowds. P. E. Easterling notes that comedy was naturally added as an offshoot to the wine and merriment, although comedy became the "black sheep" of the festival in light of the higher aspirations that Aristotle gave to Greek drama.
Aristotle created the format of tragedy in his poetics, which added further structure to the Thespian festivals. Tragedy, according to the philosopher, was not an emotional dampener but was in fact a cathartic experience for the audience, as long as the play maintained the unities -- one time, one setting and one plot -- and featured a tragic hero whose hubris, or pride, led to his nemesis, or tragic end. Ultimate catharsis, or emotional release, was, according to Aristotle, the finest achievement of the drama.
Modern Greek theater festivals still honor the traditions of Thespis, the unities of Aristotle, and plays such as Sophocles' "Oedipus Rex," one of the greatest expressions of tragic catharsis. What began as a simple wine-infested dedication to the jolliest of the gods and the rote blood sacrifice of scapegoats is the classical apex of cathartic tragedy and philosophical thought for humanity.