Answer: foil
A secondary character who functions as a contrast to a major character is a foil. In a literary work, a foil serves several purposes. Sometimes, the foil allows us to see the qualities or shortcomings of the protagonist more clearly. Other times, the foil is intended to provide an example of what a protagonist would be like if he had chosen a different path. An example of a foil is young Fortinbras in the play Hamlet.