Boo Radley is a neighbor who lives on the same street as the Finch family. Boo’s defining characteristic is his literal and symbolic invisibility. A recluse who only comes out at night, Boo becomes a receptacle for the town’s fears and superstitions. The Finch children make up strange and horrific stories about Boo, informed by the gossip of the adults. The reader understands that Boo has been mistreated by his father, who locked him up for a minor infraction when he was a young man, but Jem and Scout believe wild tales about Boo, such as the rumor that he kills the neighbors’ pets. As such, within the context of the novel Boo functions more like a ghost than an actual character. He only appears in the final chapters of the book, and even then, only speaks once, but his presence is felt throughout. In fact, Scout begins her narration saying that in order to understand the events of Halloween night it’s not enough for the reader to know the background of Tom Robinson’s trial. The reader must also know the history between Scout, Jem, and Boo Radley.
Symbolically, Boo represents both Scout’s childish understanding of the lives of people around her, and also the genuine risks and dangers that face children as they grow up in the world. As a ghost-like figure, Boo also symbolizes aspects of the town’s past, such as intolerance, inequality, and slavery. The town prefers to keep the less admirable aspects of its past out of sight, like Boo, but, like Boo, ghosts of the town’s past continue to inform the community’s present.
Boo doesn’t change as a character over the course of the novel, but Scout and Jem’s perception of Boo changes from monster to hero as they learn more about Boo and develop a sense of empathy. Boo is genuinely kind and protective of the children. In fact, he protects them when Atticus has underestimated the threat that Bob Ewell poses to Atticus and his family. Scout never makes Boo’s motives explicitly clear, but in a story that does not shy away from having unambiguously good and unambiguously evil characters, Scout clearly intends the reader to count Boo among the good ones. The decision that Heck Tate and Atticus make at the end of the novel to protect Boo’s privacy marks the culmination of the novel’s lessons about courage, empathy, community, and the law.