Mrs. Dubose, Tom Robinson, and Boo Radley are all courageous, but in different ways. None of them are obvious figures of courage.
Mrs. Dubose is first held up as an example to Scout and Jem as an example of courage. Mrs. Dubose does not seem like the first person one would think of when looking for a courageous figure. She is a grumpy old lady who is not only racist but cruel. Yet Atticus tells his kids that she is brave.
I wanted you to see something about her-I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. (ch 11)
Atticus wants his children to understand that Mrs. Dubose was brave because she knew that she was fighting an uphill battle against her morphine addiction. She wanted Jem to read to her to distract her, so she could die on her own terms. Atticus tells Scout and Jem that courage is continuing to fight when you know you’re beaten.
Tom Robinson is a strong man, but he is also fighting a near-impossible battle. He knows his verdict will not likely be reversed on appeal. He does not want to rot in jail. He decides to die on his own terms.
I guess Tom was tired of white men's chances and preferred to take his own…(ch 24)
Tom is courageous because he tries to escape—and almost makes it—rather than allow others to make his choices for him. Tom Robinson is the first of the symbolic mockingbirds—the innocent victim who is targeted.
Finally, there is Boo Radley. Boo did two incredibly courageous things. First, he was a quiet and shy man and coming out of his house was an act of bravery in itself. He not only came out, he took on a drunk man with a knife. He attacked Bob Ewell and saved Scout and Jem’s life.
I never heard tell that it's against the law for a citizen to do his utmost to prevent a crime from being committed, which is exactly what he did … (ch 30)
Throughout the book, Boo Radley slowly gains the courage to come out of the door and begin interacting with the children, usually in secret at first. By the end of the book he has taken action and actually been involved in a physical fight to save the children. He saved their lives. Boo Radley is the second of the symbolic mockingbirds. Society does not understand him, and he has been isolated and locked away for years, but he is not a bad person.