The narrator of the book. A quiet, intelligent boy who represses his feelings, often making him victim to paranoia and aggressive outbursts of emotion.
- Academic Athlete: Though initially only academic, this is what he becomes once Finny starts training him for the Olympics.
- Ambiguously Christian: In his narration, Gene makes multiple fleeting implications and allusions to Christianity and related things, suggesting that he has reasonably extensive knowledge of the religion. However, Gene never explicitly discusses his religious beliefs, and there are things that conflict with him being Christian, such as frequently using "Jesus Christ" and variations of it as a curse and only praying to impress his roommate. It seems quite possible that Gene's family is Christian, but he doesn't consider himself Christian. Also, if you believe the interpretation that the book is actually about Gene's repressed homosexuality, this could potentially provide some extra background for his homophobia, as homosexuality is often identified as a sin.
- Ambiguously Gay: Very, very obsessed with Finny, emotional and physical aspects both included. He also gives an infamous paragraph-long description of how nice Brinker's butt is.
- Author Avatar: John Knowles stated that although there's a bit of him in every character, the one based the most on him is Gene.
- Berserk Button: Insulting Finny (even indirectly, as demonstrated by Quackenbush) and trying to talk about his true nature.
- Best Friend: To Finny. Kind of.
- Beware the Nice Ones: Implied to be a relatively nice boy, if not somewhat reserved. However, his temper is not to be trifled with, and behind his stoic facade he hides a myriad of brutal insecurities and envy, leading to him indirectly murdering someone. Leper describes him as "a swell guy, until the chips are down"...
- Broken Ace: Well-liked? Check. Athletic? Check. Extremely intelligent, both psychologically and academically? Check. Incredibly jealous, insecure, emotionally unstable, and indirectly responsible for his best friend's death? Check.
- Cain and Abel: Though they are not literal brothers, many readers have compared Gene and Finny to these two. Gene is the Cain to Finny's Abel.
- Character Development: At the beginning of the book, he's paranoid, jealous, insecure, and dangerously competitive. By the end of the book he's obtained significant peace of mind, having developed the philosophy that ignorance is what pits people against each other and there's no such thing as "enemies."
- Classical Anti-Hero: He definitely fits this role, as he is often controlled by his rampant insecurities and constant fear. The entire book is about him conquering his ignorance in order to become a better person.
- The Cynic: Sarcastic, depressive, and believes human beings are fundamentally ignorant and fearful. Half of a CynicIdealist Duo, the other half being Finny.
- Deadpan Snarker: Makes some pretty snarky comments at times. He mentions that 1942 was his "sarcastic summer" and implies that his older self is not nearly as snarky.
- Emo Teen: Could definitely be considered this, since he's cynical, angsty, self-loathing, and, of course, emotional.
- Green-Eyed Monster: One of the major themes of the book is how influenced Gene is by his jealousy and the horrific consequences of this.
- Height Angst: He seems to think he's too short, although 5'8½'' isn't all that short for a boy his age anyway.
- In with the In Crowd: His narration doesn't imply he's popular at all, but he's an Unreliable Narrator. He's close to the two most popular boys in the school (Brinker and Finny), and Leper, a social outcast, is implied to desperately want to be his best friend.
- Living Emotional Crutch: Although it's always been clear Finny is this to him, he's increasingly implied to be this to Finny as well.
- Muscle Angst: He isn't very happy with the fact that he's only 140 pounds, whereas Finny is well-built and a full ten pounds heavier than him.
- Nervous Wreck: Interestingly implied to be this by Finny, even though Gene's narration itself never necessarily lets us in on this.
- Not So Stoic: Represses his emotions and, thus, generally comes off as very controlled and perhaps aloof. However, there are incidents during which his mask falls apart, such as when he fights Quackenbush for indirectly insulting Finny and when he kicks Leper over in his chair for claiming he's a "savage underneath."
- Unreliable Narrator: Tends to see things through a lens that is not very objective.
- Wise Beyond Their Years: Sort of. Teenage Gene is incredibly intelligent on multiple levels; however, as is the case with most intelligent children and teenagers, his emotional intelligence corresponds with his age.
A handsome, charismatic boy who is the best athlete in the Devon School. Extremely popular and well-loved by everyone.
- All-Loving Hero: Finny loves and sees the best in everyone. Or at least, Gene claims he does.
- Always Someone Better: As an extraordinary athlete, a charismatic charmer, and a genuinely good person, he unintentionally fulfills this role for Gene.
- Ambiguously Bi: Amongst his many friends, his connection with Gene appears to be a special one, their connection going to certain extremes that make one question if their feelings are purely platonic. He's this instead of Ambiguously Gay because in the short story Phineas—essentially the prototype of A Separate Peace—it's confirmed that he likes girls, and he talks animatedly about how he's slept with three of them.
- Bad Liar: He's a very genuine, straightforward person, so this isn't surprising. Gene says he's terrible at poker.
- Beauty Equals Goodness: Supposedly the most beautiful and most good-hearted boy in Devon, although this is according to Gene.
- Best Friend: To Gene, in a much more genuine way than Gene is to him.
- Big Man on Campus: The most popular boy in the entirety of the Devon School. His magnetic personality wins over everyone, including the stubborn, strait-laced Devon teachers.
- Book Dumb: Gets a steady procession of Ds in school and comments that no amount of studying could get him higher than a C, but is definitely not "dumb" in every respect. For example, he's actually extremely eloquent when speaking.
- Break the Cutie: It's revealed at the end of the book that Gene jouncing the limb and making him break his leg has stripped him of his carefree, confident personality, since this means he can never pursue his dream of becoming a professional athlete.
- Cain and Abel: Though they are not literal brothers, many readers have compared Gene and Finny to these two. Finny is the Abel to Gene's Cain.
- Career-Ending Injury: His broken leg. Technically his career wasn't established yet, but he seemed well on his way to fulfilling his dream of being an Olympic athlete.
- Catchphrase: Says "pal" and "naturally" a lot.
- Dumb Jock: Kind of. He's definitely a jock, as sports are his passion and he's the best athlete in the school, but he's only really Book Dumb, not dumb in general.
- Hidden Depths: At the end of the book it's revealed he's not the impenetrable, all-loving idealist we thought and is in fact suffering greatly due to the fact that he can no longer play sports or even join the War. To really drive this home, he makes several uncharacteristically cynical statements such as saying he will "hate it everywhere" if he's not in the War and he doesn't know if he can take it anymore. This is foreshadowed by what Finny accidentally blurts out at one point earlier in the book, during an argument with Gene: that he's suffered.
- The Idealist: Cheerful, optimistic, and believes anything you love will love you back. Half of a CynicIdealist Duo, the other half being Gene.
- In-Series Nickname: Finny.
- I Thought Everyone Could Do That: As he achieves athletic feats effortlessly, he tends to assume everybody has a talent that parallels his own, even if it isn't involving sports. For example, he thought, before being told otherwise, that Gene was a straight-A student just because, not due to excessive amounts of studying—much to the annoyance of Gene himself.
- It's All About Me: Rather self-absorbed, as he tends to assume Gene always wants to do the things he does, and he doesn't bother asking. Then again, Gene never tells Finny when he doesn't want to do something.
- Keet: Exuberant and outgoing, Finny wants nothing other than to have fun, and will make sure you know it.
- Living Emotional Crutch: To Gene, as a result of their unhealthily codependent relationship. Even after he dies, Gene is totally obsessed with him, or at least the memory of him.
- Lovable Jock: Both the best athlete at Devon and one of the friendliest boys there.
- Mr. Fanservice: Well, the book is told from Gene's perspective, and Gene tends to go off on long, detailed tangents describing Finny's physical beauty.
- Named by the Adaptation: In the 2004 movie, Finny is given the last name "Pell."
- No Name Given: No last name given.
- The Not-Love Interest: Finny is this to Gene. They're always together, have a very deep, almost romantic relationship, and Gene—who is obsessed with Finny, body and mind—gives physical descriptions of Finny so detailed and adoring they have sexual undertones. Although their relationship in the book is (explicitly) that of best friends, that doesn't stop people from seeing the Homoerotic Subtext.
- School Idol: Admired by all the boys at Devon, Finny is this in spades.
- Stepford Smiler: After he breaks his leg and is unable to pursue sports, his passion, Finny still acts as carefree as ever. However, near the end of the book, he starts to cry and confesses to Gene that he has indeed been suffering on the inside.
- Too Good for This Sinful Earth: According to Gene, Finny is one of the few truly good people in the world, as well as one of the few people who isn't controlled by fear or spite. However, with the reveal that he is a Stepford Smiler, we really have to emphasize the ''according to Gene'' part.
- What Beautiful Eyes!: Has striking blue-green eyes.
The witty, popular class politician with an attitude and a devotion to justice. Initially dresses conservatively and takes part in many community service-type clubs, but eventually becomes more of a rebel.
- Big Man on Campus: He's one of the most popular boys in the class. Gene mentions that there are very few boys at Devon who dislike Brinker.
- Character Development: In spite of what those high school study guides would have you think, Brinker can't be considered a completely static character. Throughout the book, he does realize that war isn't just a game to play at.
- In-Series Nickname: Is eventually nicknamed Yellow Peril by Finny due to a joke about him actually being Madame Chiang Kai-Shek.
- Like Father, Unlike Son: His father acts like war is a game and insists that flaunting your war experiences when you're older is the best way to make people respect you. In the beginning, Brinker has a similar attitude. However, after his Character Development, Brinker is resentful of his father's perspective on war, believing himself that it is pointless and awful.
- The Nicknamer: It's mentioned by Gene that he spends his time at Devon creating nicknames for other boys while avoiding being assigned one himself.
- Not So Above It All: Usually acts like he's above Finny's antics, but willingly helps organize Finny's Winter Carnival after becoming more rebellious.
- Only Sane Man: Well, Finny's a Stepford Smiler who immerses himself in delusions and conspiracies to remain carefree, Gene indirectly murders Finny, and Leper becomes severely mentally ill after enlisting in the army. So this sounds about right.
Elwin "Leper" Lepellier
A friendly, unassuming boy who loves animals and nature. Clearly an outsider, as he is frequently made fun of by the other boys and tends to hang out by himself. After enlisting in World War II and subsequently losing his mind, he changes significantly, becoming bitter and emotionally erratic.
- Adorkable: He's a mild-tempered, glasses-wearing boy who loves animals and nature, so absolutely! Unfortunately, this trope is no longer applicable after he...loses his mind.
- Break the Cutie: What enlisting in the War does to him. Formerly a kind, tranquil boy, he begins hallucinating, breaking into fits of laughter, and just outright weeping. He also loses his manners, deciding other people aren't worth being polite to.
- The Cutie: Since he's a soft-spoken boy who loves animals and doodles during class, it's easy to see him as this. Until he goes crazy.
- Hidden Depths: He's viewed for most of the book as an odd Nature Lover who is made fun of by the other boys, though he remains an oblivious Nice Guy. However, after he enlists in the War he stops being polite on account of other people, and he reveals that he actually holds resentment for the boys that constantly mocked him.
- In-Series Nickname: Leper, which both looks similar to his last name and alludes to his position as a social pariah at Devon—although it's doubtful the boys who gave him this nickname were thinking of that second part.
- Nature Lover: Enjoys walking through forests and photographing beaver dams. What more do you need?
- No Respect Guy: Constantly mocked by the other boys, even though he's one of the nicest people in the school. This is originally played off as an unimportant relationship dynamic at Devon that Leper himself is oblivious to, but it's Played for Drama when it's revealed he actually understands that nobody respects him and secretly resents it.
- Only Known by Their Nickname: Though the other boys seem to know his real name, nobody ever calls him anything but Leper. Gene comments at one point that Leper would not remember to answer to any other name.