Greek Theater originated with the followers of Dionysus, the god of fertility and wine. A form of drama started as his followers danced and sang stories of Greek myth. Thespis, a priest of Dionysus, is credited with giving birth to Greek theater when he introduced the dialogue component. He would engage in dialogue with the chorus, in effect becoming the first actor. In 534 B.C., the first competition for tragedy was held in Athens during the City Dionysia, the four day festival held in honor of Dionysus. Greek comedy originated during the Lenaea, a three day festival held in Athens during the month of January, in 486 B.C.
Greek theater consisted of two types of drama: tragedy and comedy. Tragedy and comedy were differentiated in two ways. The Aristotelian tradition holds that tragedy was concerned with the transition of noble people from good to bad circumstances and comedy was concerned with the transition of the average person from bad to good circumstances. The rhetorical tradition defines comedy as fiction that is believable and tragedy as fiction that is not believable.
The theatrical competition held during the City Dionysia lasted the full four days of the festival. Four playwrights were chosen to compete. Each playwright was charged with writing three tragedies and one satyr. Each author had their four plays performed during the course of one day. At the end of the four days, a winner was chosen. These plays are believed to have been first performed with the audience seated on the slope of a hillside. Theaters were built later.
The heavyweights of early Greek tragedy are Aeschylus, Sophocles and Euripides. Aeschylus added a second actor and first developed the concept of a trilogy. Seven of his 80 plays survive. Sophocles added a third actor and personalized his plays making them more complex with personal interaction between the characters becoming more center. He is thought to have written about 120 plays with only seven surviving. Euripides introduced an unconventional view of Greek myth that influenced later schools of drama. Nineteen of his plays survive. Aristophanes is considered the genius of Greek comedy and 11 of his plays survive.
The ancient Greeks did not define comedies as "funny" plays nor were tragedies plays with tragic endings. In fact, there were a fair amount of comedies that were not funny and tragedies that had happy endings.