Throughout the novel, Atticus is revealed through the eyes of Scout, his young daughter; Scout, the narrator, is telling the story from much later, though. That perspective affects how readers gain access to him.
Scout goes to him with questions, and how he handles these moments shows different aspects of his character. One constant in these interactions is Atticus listening to Scout and taking her very seriously. For example, when Scout asks him if their family is poor, Atticus replies, "We are, indeed." He then proceeds to explain to Scout how the Great Depression has affected different people differently. He proves to be caring, intelligent, and thoughtful. He later explains the case he is trying in court to his brother, and we learn something Scout learns years later: that Atticus meant for Scout to hear the whole explanation. This scene develops Atticus's wisdom.
Scout has great admiration for her father, but she also views him as old and somewhat removed. Harper Lee develops a world in Atticus his children do not know when the rabid dog comes to town. The threat is real, and in the moment, the sheriff puts the fate of the town in Atticus's hands, shocking Scout and Jem. When Atticus accurately shoots the ill and dangerous dog, saving the town, Scout and Jem see his hidden talents and more physical strength in him than they had previously thought possible. With this scene, Lee hints at what we readers (and in truth Scout as well) do not know about Atticus.
Lee also builds Atticus's compassion and sense of morality throughout his time as Tom Robinson's lawyer. He takes the racially charged case despite the difficulties to him; some in the town do turn against him, and he is almost attacked by a mob at the jail one night. He also treats Mayella Ewell with compassion, showing he sees the complexities of the social system in Maycomb. His clear moral compass, though, draws a line at pitying her at the expense of Tom's freedom.