The chief character who is not what he appears to be is Boo Radley. Jem, Scout, and Dill are afraid of him through much of the novel because he comes from a reclusive family and is almost never seen. They have also heard a story that he stabbed his father in the leg with a pair of scissors, making Boo seem a dangerous and unpredictable character. His house, near the Finch house, has the quality of a haunted house, and Boo seems to the children to be ghostly and spooky.
However, despite their fear of him, the children find out that Boo is, in fact, looking out for them. He puts a blanket around Scout's shoulder during the fire that burns down Miss Maudie's house. Later, he protects the children from Bob Ewell.
Mrs. Dubose: Jem and Scout hate their neighbor Mrs. Dubose because she is always insulting them in nasty ways. However, when Atticus forces them to read to her, they learn that she is a dying woman determined to shake a morphine addiction. They come to have a new respect for her courage and integrity.
Atticus: Just at a moment when Scout is feeling that Atticus is elderly and boring and has less to offer than the parents of her school peers, she discovers that Atticus is a courageous sharp shooter. She recognizes this when he is called in to shoot a rabid dog. Scout comes to see him in a new light as a person of great skill but modest about his God-given gift.
Walter Cunningham: At first, Mr. Cunningham leads a mob that wants to lynch Tom Robinson. However, after he is a member of the jury for Robinson's trial and hears what really happened, he wants to fully acquit Robinson. The children are surprised at his change of heart and find that he, too, is not what he seemed at first.
Calpurnia: Scout sees a new side of Calpurnia when she takes the children to her church. Scout learns that Calpurnia can speak African American dialect as well as the standard English she uses when working for the Finches. She comes to realize too that Calpurnia is embedded in a community outside of and apart from the Finch household.
1. Boo Radley appears to be a complete social misfit, a boogey-man, a character of nightmares and childhood dare-games. He is supposedly evil, a criminal, a spook, and completely devoid of any normalcy. However, we see that this is not the case. He tries to befriend Scout and Jem; he is kind and attentive as he gives them presents in the tree. He enjoys laughing and being happy as evidenced by the chuckles when Scout falls out of the tire. He is caring and understanding when he sews Jem's pants and returns them without his father knowing. He comes out of his shell to defend and protect the children at the end--the only one in the neighborhood to do so. Boo is a kind hero.
2. Mrs. Dubose appears to be a cantankerous old lady who is bitterly mean to the core, without an ounce of goodness or integrity in her. She picks on the kids, is a bitter racist, and meddles. However, as Jem learns later, she undertook a very courageous battle to kick her morphine habit. She fought hard until she beat it, showing more courage than a lot of other people would have. It turned out she did have goodness, a sense of humor (in giving Jem the flower), integrity and grit.
3. Mayella Ewell appeared to be a cowardly tattle-tale who was simply the product of a white trash family. She appeared to be despicable, a low-life, and a no-good member of society. However, we learn more about her--she was lonely, she wanted friends, she wanted to improve her station in life (she kept red flowers in her trashed yard), and she was trying to be kind to others. She still made poor choices in the end, but there was more to her than the stereotypes would have dictated.
4. Tom Robinson, accused of raping a white woman, appeared to be, on the surface, and evil man who had done evil things. If one didn't take the time to go to the trial or to understand the Ewell's, you would assume he was an awful man. However, he was kinder to the Ewells than most people, trying to help Mayella out, and was in no way shape or form a criminal. He was a decent, hardworking kind man trying to do what was right and just caught in a bad situation.
5. On the surface, the men who came to the jail in an angry mob, during the day, were decent, hard-working folks who tried to do what was right. However, under that surface lurked vicious racists who would be willing to harm an innocent black man just because he was black. Walter Cunningham made the right choice, and tapped into his inner good self, and walked away from the situation.
I hope that those thoughts help a bit; good luck!