Deuteragonist

The issue is no longer about the artistic representation of woman going on within the story: rather, the art object, now unrelated to the actual woman (at a literal level, at any rate), becomes her deuteragonist and antagonist, and the opposition thus settled becomes further complicated by reversal, exchanges, shifts in their respective positions.

Source: wiktionary

The first disposition accords with the attested reality of Nero acting in masks resembling his own features or those of women with whom he was in love (Suet. Nero 21.3), especially Poppaea (Dio 63.9.5), and generates a set of roles for the deuteragonist all of which focus on failed counsel; it also underlines the parallelism between the Seneca-Nero and Nero-Prefect scenes, and reinforces the view that the First and Second Prefect are not identical.

Source: wiktionary

In the distribution of the other roles between the deuteragonist and the tritagonist, the same criteria must have applied. When two characters had an important part in a tragedy and could not be played by a single protagonist, the second was played by the deuteragonist.[…]The tritagonist, even more than the deuteragonist, had to play several secondary roles.

Source: wiktionary