Many of the characters in To Kill a Mockingbird are found to be much different than the first impressions received by Jem and Scout. Boo Radley is the most obvious example. He goes from being a bloodthirsty killer of small animals to a heroic neighbor who saves the lives of the children at the end of the novel. Scout finally sees the real Boo after she escorts him back home in the final chapter.
Atticus was right. One time he said you really never know a man until you stand in his shoes and walk around in them. (Chapter 31)
Dolphus Raymond is another character whose actions belie his true motives. Most of Maycomb is convinced that Dolphus is a drunk with mental instability, but Jem and Scout come to find that it is all a put-on: Mr. Raymond deliberately weaves about the town sucking on a straw from a bottle hidden in a bag; he believes it gives the townspeople an excuse to explain "why he lives the way he does." Even minor characters like Dick Avery are not always what they seem. Avery seems to enjoy sharing gossip with Miss Stephanie, and his only talent seems to be his proficiency in long-distance peeing. He blames Jem and Scout for the unseasonable snow in the morning, but plays the hero later that night, barely escaping with his life after being the last man out of Miss Maudie's burning house. Scout's classmate, Little Chuck Little, is another example. He
... didn't know where his next meal was coming from, but he was a born gentlman... He was among the most diminutive of men... (Chapter 3)
It is Little Chuck, the smallest child in the class, who stands up to Burris Ewell--with his hidden knife in hand--in defense of Miss Caroline.