Captain John Yossarian is the book's protagonist, a 28-year-old air force bombardier who is stationed on a small Italian island toward the end of World War II. Yossarian has flown many combat missions, and he's beginning to think it's time to stop. Unfortunately, the only way he can be sent home is to prove he's crazy—and wanting to be sent home proves that he's sane. This is the rule called "Catch-22." Determined to live forever or die trying, Yossarian dedicates himself to fighting the system. As the combat missions continue, Yossarian loses more and more friends and begins to break down emotionally.
Although the gunner Snowden dies before the book's action begins, recurring memories of his death are crucial to Yossarian's own story. Snowden died terribly, and Yossarian was unable to save him. A final memory of Snowden's death helps Yossarian face his own fear of dying; it also shows Yossarian that he must create a life that will honor his dead friends.
Doc Daneeka was an internist on Staten Island, New York, before being caught in an outrageous attempt to declare himself unfit for service. He introduces Yossarian to Catch-22, the rule that prevents Yossarian from going home. The doctor is terrified of flying and comes up with a scheme that will allow him to draw his army pay without having to get into a plane. The scheme backfires, and Doc Daneeka is declared dead as a result of an administrative error.
Milo, the squadron's mess sergeant, sets up a black-market syndicate that becomes fabulously successful. His only goal in life is to make a profit; he even contracts with the Germans to bomb his own squadron. The only person he trusts is Yossarian, and that's only because he's not afraid Yossarian will steal from him. Milo is a sympathetic character for much of the book, but his selfishness and greed finally make him a repellent one.
Chaplain Tappman is a shy, awkward man who never manages to fit in. He frets over inconsistencies in the Bible and allows himself to be bullied by his assistant. He and Yossarian slowly become friends. By the end of the book, the chaplain has found enough confidence to help Yossarian choose an honorable path in life instead of a self-destructive one.
Nately is an innocent 19-year-old lieutenant from a wealthy family. He tags along with Yossarian and his friends on trips to Rome, where he naively falls in love with a prostitute who has no interest in him. Nately manages to maintain his idealism even as he's drawn into her world. He never accepts the fact that his life with the prostitute can't have a happy ending.
Lieutenant Aardvark, known as Aarfy, is a blandly affable frat-boy type. He's Yossarian's navigator, and a bad one. Though his mistakes repeatedly lead the men into danger, Aarfy never loses his composure. As the story progresses, readers gradually realize that Aarfy is a sociopath with a total inability to understand other people. He rapes and murders Michaela, a young Italian woman.