Which characters are foils in A Separate Peace?

A Separate Peace is a frame narrative through the eyes of the main character, Gene Forrester. The novel tells about his time in boarding school fifteen years earlier, through themes of friendships, death, and growing up. Knowles uses Gene and his friend Phineas (Finny) as dramatic foils: characters whose differences are highlighted to bring out their different qualities. Through Finny's outgoing personality, we are able to learn more about Gene.
In the novel, Gene is a hardworking, rule-following student, so, as a foil, Finny is his opposite. Finny is more charismatic and athletic, and he often finds ways to break the rules. While his foil Gene tends to be more reserved, Finny is always the center of attention and everyone's friend.
While they are best friends, Gene often finds himself admiring Finny and is also jealous of his friend. It is this dilemma that most likely leads to Finny's fall. Gene both loves and resents his best friend. When Finny is out on the tree branch, Gene jostles it just enough so that his friend falls and breaks his leg.