Jake Barnes was injured during World War I, resulting in his impotence. During his recovery he fell in love with his nurse, Brett, but because of his injury they cannot consummate their relationship. Like many young people after the war, Jake is disillusioned and depressed. He moves to Paris to live as a writer, although he prefers to spend his time drinking and partying. As a member of the lost generation Jake focuses on distracting pleasures, such as food, drink, and travel, to fill a spiritual void. To compensate for his impotence, Jake studies traditionally masculine sports such as boxing, fishing, and bullfighting.
Lady Brett Ashley inherited her title from her husband, a British lord, whom she is divorcing as the novel opens. Brett, like many in the lost generation, experienced trauma during the war; she was a nurse in a military hospital; her husband, a wartime sailor, was abusive toward her. Her relationship with Jake is frustrating because of his impotence. Brett derives great pleasure from male attention, and she enjoys having men compete for her affection. She also pushes back against social expectations at every turn; she keeps her hair boyishly short, sleeps with anyone she likes, and ignores social niceties such as showing up on time. Despite her free-spirited ways she constantly complains of feeling miserable. Because the novel is told from Jake's perspective, it's unclear what or who might make Brett happy. Jake seems to think he could, if not for his impotence; but the way Brett treats him—standing him up, flaunting her affairs in front of him, and calling him only when she needs something—suggests she is manipulating him as she does all her other conquests.
After Robert Cohn's brief affair with Brett, he refuses to see the dalliance for what it is; he follows Brett around and moons after her, attempting to maintain a relationship when she is no longer interested. Through his narration Jake depicts Cohn as petulant and childish; he is easily controlled by a strong woman like Brett. He is the opposite of the masculine type Jake feels Brett needs. Jake disrespects Cohn for this perceived weakness; he also views Cohn as less than a real man because he never served in the war and because he is Jewish.
The 19-year-old bullfighter Pedro Romero embodies the masculine ideals Jake values, making him—in Jake's mind—the only worthy match for Brett. Many view Romero as a bullfighting prodigy; the Spanish hotel owner Montoya calls Romero "a real one." Romero understands the bulls more intimately than any of the other fighters do, and he gives audiences a real thrill rather than the illusion of one. Brett is immediately attracted to Romero's passion and claims to love him; because Jake respects and admires Romano he helps Brett sneak away with him. At the end of the novel Romero tries to change Brett into a more traditional woman, so she leaves him, claiming she is afraid of destroying him.
Bill Gorton enters the story drunk and forgetful, bringing a touch of humor to the proceedings. Throughout the novel Bill's comical ways dispel rising tension between the other men, all of whom are competing for Brett's affection. Because Bill doesn't take part in this competition it's possible he is gay. Jake feels no rivalry with Bill, aside from their friendly fishing competitions; thus he feels free to make himself vulnerable with Bill, telling him things he would never discuss with other characters.
Mike Campbell is Brett's fiancé, yet the details of their relationship are somewhat confusing. Despite being a perfect Hemingway alpha male—a strong, heavy drinking war veteran—Mike is weak in love. He stays with Brett despite her constant cheating and disrespect, even allowing her lovers to join them on vacation. The novel implies Mike drinks to forget what he's seen on the battlefield, which he never discusses, or the fact he's completely bankrupt, but his self-pity and anger toward Brett also likely influence his drinking. For the most part Mike ignores Brett's dalliances with other men, but her relationship with Cohn enrages him, partly because Cohn is Jewish and partly because Cohn doesn't recognize when the fling is over. This rage boils over in Spain when Mike goads Cohn into a fight, which Mike promptly loses.