What did the children know of Atticus's nature before the trial in To Kill a Mockingbird?
Before the trial, the children know that Atticus is wise, persistent, courageous, and fair.
Atticus is wise because he teaches the children lessons about how to get along with people. Atticus tells Scout that you can never really understand a person "until you climb into his skin and walk around in it" (ch 3). He wants them to learn empathy. He also teaches them to treat all people well, regardless of their social class or race.
Atticus is also persistent. Even when all of the other people in the town seem to be against them, Atticus sticks to his guns. He tells Scout, "I'm simply defending a Negro…” and tells his children to keep their heads (ch 9). He does not give up even when a mob tries to lynch Tom Robinson.
Shadows became substance as lights revealed solid shapes moving toward the jail door. Atticus remained where he was. The men hid him from view. (ch 15)
Atticus sits outside Tom Robinson’s cell, and refuses to leave when the mob shows up.
Atticus is also courageous because he stares down the rabid dog and shoots it in one shot, when everyone else is afraid to do so.
With movements so swift they seemed simultaneous, Atticus's hand yanked a ball-tipped lever as he brought the gun to his shoulder. (ch 10)
Atticus stands up to the mad dog and protects the town the same way as he stands up to the metaphorical rabid dog of racism.
Atticus is fair. During the trial, he defends Tom Robinson with all his ability. He proves that Bob Ewell is lying, and that Tom could not have physically committed the crime. He almost shames the jury into acquitting him.
“I am confident that you gentlemen will review without passion the evidence you have heard, come to a decision, and restore this defendant to his family. In the name of God, do your duty." (ch 20)
In the end, Atticus loses. However, he makes the town think about race for real, and he does succeed in convincing everyone that Tom is innocent—even if he cannot get him acquitted.