Tritagonist

The tritagonist is "the third most important [character] of a narrative, after the protagonist and deuteragonist." The word is the Ancient Greek tritagōnistḗs, "third actor," and in ancient Greek drama the tritagonist was "the third member of the acting troupe." The role mattered structurally: shifting adversary parts to a third actor freed the deuteragonist to play confidant, deepening the protagonist's scenes, and the role "would typically go to a performer with a voice in the bass range," after the tenor protagonist and baritone deuteragonist. The article's named tritagonists are performers: Aeschines, whom Demosthenes judged untalented in the role, and Myniscus, tritagonist under the playwright Aeschylus.

In modern use the term ranks a story's third figure: the love interest, the rival, the mentor, whoever stands one rung below the second lead. Naming that rung is an ensemble-cast decision, which view to give a chapter and how much interiority to spend, covered in managing an ensemble cast.