noun
foil; person who makes someone else look better
Refers to a person whose role is to make another person stand out or appear more attractive by comparison. Often used in social, entertainment, or comedic contexts.
彼はいつも友達の引き立て役に回っている。
He always ends up playing the foil to his friend.
お笑いコンビで
In a comedy duo, the balance between the funny man and the straight man is important.