The correct answer is Foil
Step-by-step explanation:
In literature, a foil character is a type of character that has a minor role in the development of the story; however, this type of character supports the development or actions of the main character or protagonist which includes highlighting the positive qualities of the main character by displaying opposite traits. Considering this, Carlo can be classified as a foil, not only because his role in the story is minor (opposite to the one of the antagonist/protagonist) but also because Carlo display traits that highlight the ones of the main character.