What impact does Boo Radley have in TKAM?

Boo is an integral part of To Kill a Mockingbird. From the start, he is a mystery that needs to be solved. He's an enigma, a legend, the scarey story people refer to at campfires. But as time goes on, we see his character become sympathetic and human; we see the goodness of a misunderstood outcast; and finally we see him as simply another example of the mockingbird.

Scout, Jem and Dill change in response to their interactions with Boo. They learn that things aren't always as they appear. They learn to open themselves up to things they do not understand in an attempt to understand. Boo's presence changes those around him.