In the novel To Kill a Mockingbird by Harper Lee, Boo Radley had a huge impact on the character development of both Jem and Scout. He taught them that one cannot judge a person on based on something as insubstantial as rumors. Rather judgements should be made based upon their actions.
The children were terrified of the stories they'd heard this about this ghostly neighbor. They were so terrified, that Jem was dared to sneak into the yard and touch the Radley House. Scared beyond belief, Jem tore his pants on the Radley fence while trying to escape. He left them there, but they were soon returned all sewn up.
When Miss Maudie's house was on fire, and the kids were sitting shivering in the freezing temperatures, a silent friend gently placed a warm blanket around their shoulders unbeknownst to them. Boo also left the children treats in the hollow tree until his brother filled the hole with concrete. This was the end of their interaction with Boo until he saved Jems life by killing Bob Ewell.
So they learned that Boo was not some evil entity. Rather he was a gentle souled mockingbird, and once they learned what it was like to walk in Boo's shoes. This lead them to realize one cannot be judge or should not be judged by anything other than their actions.
Throughout the novel, Jem and Scout's perspective on Boo Radley changes as the story progresses, which helps develop their characters. Initially, the children fear their reclusive neighbor and believe the rumors surrounding Boo. Jem becomes fascinated with the idea of seeing Boo and even creates a game where the children act out Boo Radley's life story. As the novel progresses, Jem and Scout mature and begin to view their neighbor in a different light. Jem and Scout begin to realize that Boo is not the malevolent phantom that they once believed he was and develop empathy for their neighbor. Towards the end of the story, Jem and Scout regret bothering their neighbor when they were younger and realize that he is just a kind, shy individual. Throughout the novel, Atticus teaches his children important lessons on perspective, sympathy, and respect. Jem and Scout both learn the importance of defending innocent beings and begin to view Boo Radley as a symbolic mockingbird. Through their interactions with Boo Radley, Jem and Scout's maturation and new perspectives are evident, which helps develop their characters.