Readers are introduced to the almost mythical character of Boo Radley in the first chapter. Recounting the little history known about the man who remains unseen, Jem tells Scout what he has learned from Miss Stephanie Crawford:
Boo was sitting in the livingroom cutting some items from the Maycomb Tribune to paste in his scrapbook. His father entered the room. As Mr. Radley passed by, Boo drove the scissors into his parent's leg, pulled them out, wiped them on his pants, and resumed his activities. Mrs. Radley ran screaming into the street that Arthur was killing them all, but when the sheriff arrived he found Boo still sitting in the livingroom, cutting up the Tribune. He was thirty-three years old then.
Mr. Radley refused to have his son committed to an "asylum" and noted that he was just high-strung at times. Boo wasn't charged with anything, as his father told the police that he was not a criminal. Of course, all of this information has to be considered through the lens of the reporter, Miss Stephanie, who is a gossip and loves to stir up trouble.
The children are fascinated with this man they have never seen, and one day, they decide to write a note and attempt to deliver it to Boo himself. They are caught red-handed by Atticus, who gives them a stern lecture, which is pretty rare for Atticus's parenting style:
What Mr. Radley did was his own business. If he wanted to come out, he would. If he wanted to stay inside his own house he had the right to stay inside free from the attentions of inquisitive children, which was a mild term for the likes of us. How would we like it if Atticus barged in on us without knocking, when we were in our rooms at night? We were, in effect, doing the same thing to Mr. Radley. What Mr. Radley did might seem peculiar to us, but it did not seem peculiar to him.
Atticus patiently tries to explain that, although Boo is different from the average Maycomb citizen, he deserves to be respected. This is the second time Atticus has caught the kids "tormenting" Boo, and he wants to make a clear impression on them this time that their antics will not be tolerated.
In chapter 23, Jem has matured and is wiser to the way the world works—which often isn't based in fairness. He is deeply troubled about Tom Robinson's conviction in spite of the clear evidence supporting his innocence, and he makes this comment:
Scout, I think I'm beginning to understand something. I think I'm beginning to understand why Boo Radley's stayed shut up in the house all this time . . . it's because he wants to stay inside.
Jem has learned to empathize with the reclusive Boo Radley. He understands that the world isn't a place of fun and games for adults and that it is often a place of pain and misunderstanding. He can finally see some reasons that Boo wouldn't even want to be part of it.
At the very end of the novel, Scout gets to have the conversation with Boo that she's always longed for, brief though it is:
"Will you take me home?"
He almost whispered it, in the voice of a child afraid of the dark.
I put my foot on the top step and stopped. I would lead him through our house, but I would never lead him home.
"Mr. Arthur, bend your arm down here, like that. That's right, sir."
I slipped my hand into the crook of his arm.
He had to stoop a little to accommodate me, but if Miss Stephanie Crawford was watching from her upstairs window, she would see Arthur Radley escorting me down the sidewalk, as any gentleman would do.
This man who has saved Scout and Jem's life emerges from his house only because he senses the danger the siblings are in. After he has rescued them, he returns to his typical personality, afraid to be outside the safe confines of his house. His voice is barely audible, and he needs Scout's assistance to get him safely home. When he arrives home, he simply releases Scout's hand, goes inside, and shuts the door. Scout never sees him again.
Boo is a great mystery who proves to be Scout's hero in the end. Although he is not physically seen until the final pages, his character is a constant background story in the children's lives.