How does Leper from A Separate Peace help support or illustrate a theme in the novel?
Leper is the character who exposes the truth of the war, Finny's accident, and the boys themselves. Leper enlists in the military because the ski troops enlistment film put a "friendly face" on the war. But the reality of bootcamp completely breaks him, and he is given a Section 8. Even though Gene never truly believed Finny's myth that the war was only a fiction created by fat old men or that Leper was a superhero in his skiis fighting the Germans all over the globe, Gene finds it difficult to face the effect that bootcamp has had on Leper.
It is Leper who also knows the truth of Finny's accident. He saw one figure on the tree jostle the limb. Leper's testimony at the mock trial convinces Finny that Gene is responsible for Finny's fall, that he did indeed jostle the limb.
Lastly, Leper tells Gene that he really is a "savage underneath," and this is true of each of the boys, and it is this part of himself that Gene must come to terms with.