Answer:
A foil.
Step-by-step explanation:
In literature, it contrasts with a character, especially the protagonist. It does this to highlight the particular qualities of the other main character.
A foil could be the exact opposite of the character or similar with a distinctive difference in some particular aspects.
The word came from the old practice to put foil in the back and gems in front in order to make them shine more brightly.
I hope this answer helps you.