The actors in ancient tragedies were hired and paid by the state and assigned to the tragic poets probably by lot. By the middle of the fifth century three actors were required for the performance of a tragedy. In descending order of importance of the roles they assumed they were called protagonist first actor (a term also applied in modern literary criticism to the central character of a play), Dueteragonist second actor and tritagonist third actor . The protagonist took the tile of the most important character in the play while the other two actors played the lesser roles. Since most plays have more than two or three characters (although never more than three speaking actors in the same seen), all three actors played multiple roles.
In modern literary criticism, the term protagonist refers to the central character of the play, not the actor. Since women were not allowed to take part in dramatic productions, male actors has to play female roles. The playing of multiple roles, both male and female, was made possible by the use of masks, which prevented the audience from identifying the face of any actor with one specific character in the play and helped eliminate the physical incongruity of men impersonating women. The masks with subtle variations also helped the audience identify the sex age and social rank of the characters. The fact that the chorus remained in the orchestra throughout the play, and sang and danced choral songs between the episodes. Allowed the actors to exit after an episode in order to change mask and costume and assume a new role in the next episode without any illusion-destroying interruption in the play.
The main duty of an actor was; of course, to speak the dialogue assigned to his characters. This however, was not the only responsibility of the actor. He occasionally had to sing songs solo of with the chorus or with other actors. The combination of acting and singing ability must have been as rare in the ancient world as it is today.