In literature, the deuteragonist (/ˌdjuːtəˈræɡənɪst/ DEW-tə-RAG-ə-nist; from Ancient Greek δευτεραγωνιστής (deuteragōnistḗs) 'second actor') or secondary main character[1] is the second most important character of a narrative, after the protagonist and before the tritagonist.
[3] The deuteragonist may switch between supporting and opposing the protagonist, depending on their own conflict or plot.
[4] Ancient Greek drama began with simply one actor, the protagonist, and a chorus of dancers.
The playwright Aeschylus introduced the deuteragonist; Aristotle says in his Poetics: Καὶ τό τε τῶν ὑποκριτῶν πλῆθος ἐξ ἑνὸς εἰς δύο πρῶτος Αἰσχύλος ἤγαγε καὶ τὰ τοῦ χοροῦ ἠλάττωσε καὶ τὸν λόγον πρωταγωνιστεῖν παρεσκεύασεν Kaì tó te tôn hupokritôn plêthos ex henòs eis dúo prôtos Aiskhúlos ḗgage kaì tà toû khoroû ēláttōse kaì tòn lógon prōtagōnisteîn pareskeúasen
He also curtailed the chorus and made the dialogue be the leading part.Aeschylus' efforts brought the dialogue and interaction between characters to the forefront and set the stage for other playwrights of the era, like Sophocles and Euripides, to produce many iconic plays.