The comedy/tragedy masks represent the masks that were worn in ancient Greece from approximately 500 B.C. to 300 B.C. During this time, plays were mostly written for a yearly festival that honored the god of wine, Dionysus, and they were either comedies or tragedies. The two masks are now used as a symbol of theater.
All of the actors in these plays were male, so they wore the masks to show a change in character or a change in mood. During the annual festival to honor Dionysus, wealthy individuals were chosen to fund the play, costume the characters and train the actors. It was considered a public and religious duty.