Foil
A dramatic character who enhances or deflates another character by contrast. Based on the literal jeweler’s foil, or black velvet cloth held behind a piece of jewelry to allow it to shine in contrast. Horatio, in Shakespeare’s Hamlet, represents the definitive foil to Hamlet. Foilis a character who is different from another character and the foil character's difference highlights the qualities of the other character, which most of the time is the protaganoist. Another way to interpret a foil character would be to explain them as a sidekickwith a contrasting personality.