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.