How does Harper Lee present the character of Atticus?
Lee presents Atticus as a humble, wise, thoughtful man. He raises two children on his own (with Calpurnia's help) and teaches them the ways of the world as if he were teaching adults. Atticus is able to understand the different perspectives of different people in town. Although he does not approve of some, he forgives bad behaviors of others because he understands that behavior comes from a host of other problems. For instance, in Chapter 23, Atticus reveals that Bob Ewell spit on him at the post office. Jem is irate and worried about what Bob might do next. Atticus tells Jem to consider Bob's perspective of things.
Jem, see if you can stand in Bob Ewell’s shoes a minute. I destroyed his last shred of credibility at that trial, if he had any to begin with. The man had to have some kind of comeback, his kind always does. So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that’s something I’ll gladly take.
Such wisdom and generosity makes Atticus sound close to a saint.
Atticus never brags about his skill as a marksman. He only uses when it is necessary. He is consistent. In other words, his words and behavior are the same no matter where he is or what situation he is in. In Chapter 9, Jem asks Atticus why he is defending Tom, even if there is little chance of winning. Atticus responds:
The main one is, if I didn’t I couldn’t hold up my head in town, I couldn’t represent this county in the legislature, I couldn’t even tell you or Jem not to do something again.
In other words, Atticus always acts according to his principles. If he doesn't defend Tom (the right thing to do), he feels he would lose his credibility. Atticus always aims to do the right thing. He tries to teach Jem and Scout to do the same.