What is the name of Holden's deceased younger brother?

Holden’s deceased younger brother is named Allie Caulfield.

Allie died of leukemia on July 18, 1946, when he was eleven years old. Although he never appears alive in the novel’s present-day events, his memory shapes Holden’s emotions, relationships, and view of innocence. Holden was thirteen when Allie died and describes spending the night breaking the windows of the family’s garage in grief and anger.

Allie’s most important keepsake is a left-handed baseball mitt covered with poems written in green ink. Holden treasures the glove because it combines Allie’s love of baseball with his creativity and individuality. Holden later writes a composition about it for his roommate Ward Stradlater, but Stradlater’s dismissive reaction intensifies Holden’s distress.

Readers sometimes confuse Allie with Phoebe, Holden’s younger sister, or D. B., his older brother. James Castle is another student connected to Holden’s memories, but he is not a member of the Caulfield family. Allie’s death is central to Holden’s unresolved grief.