Antagonist is to foil as protagonist is to ___________?

Question

More specifically, I'm writing a paper about the play/film "Wit," and I'm trying to determine the literary "role" of the character Susie Monahan. She's an advocate for the protagonist, Vivian Bearing.

Any insight would be much appreciated!

Answer 1

I would say hero.

Answer 2

glad wrap

Answer 3

erm... supporting character? I would just call her an advocate or friend. She could well be a foil if she has opposite aspects of Vivian.