In an ancient Greek drama, what was the second most important character called?

In literature, the deuteragonist or secondary main character (from Ancient Greek: δευτεραγωνιστής, deuteragōnistḗs, second actor) is the second most important character, after the protagonist and before the tritagonist. The deuteragonist may switch between supporting and opposing the protagonist, depending on the deuteragonist's own conflict/plot.

Because Ancient Greek drama involved only three actors (the protagonist, deuteragonist, and tritagonist) plus the chorus, each actor often played several parts. For instance, in Sophocles' Oedipus Rex, the protagonist would be Oedipus, who is on stage in most acts, the deuteragonist would be Jocasta (Oedipus' mother and wife), as well as the Shepherd and Messenger. This would be because Jocasta is certainly a major role (acting opposite Oedipus many times and occupying a central part of the story) and because the Shepherd and Messenger are onstage when Jocasta is offstage.