Innocence is an important theme in To Kill a Mockingbird, and the characters that are most often linked to this theme are Boo Radley and Tom Robinson. Readers might also see innocence in Scout and Jem Finch, who transition from childhood innocence to a greater understanding of the world around them. However, a strong case can also be made for Atticus as an innocent character, though his innocence manifests in ways different from the other innocent characters in this novel.
A kind, decent man with scarcely a bad word to say about anyone, Atticus is mercifully free of the kind of small-minded prejudices held by most of the inhabitants of Maycomb. He possesses a remarkable capacity for empathy, and this allows him to look for the good in people, even in unpleasant characters like Mrs. Dubose. Ultimately, Atticus's very best traits—his compassion, empathy, and faith in humanity—are what make him innocent and, at times, a bit naive.
Atticus's tendency to look for the best in others is generally a good thing, allowing him to earn the friendship and respect of all different types of people. At the same time, however, his own inherent goodness occasionally blinds him to the genuinely evil intentions of others. The best example of this is Atticus's attitude toward Bob Ewell. After Tom's trial, Bob Ewell is enraged with Atticus, going so far as to publicly threaten to kill him. Scout and Jem are seriously worried about what Bob might do, but Atticus doesn't take his threats seriously:
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. . . . We don’t have anything to fear from Bob Ewell, he got it all out of his system that morning.
Atticus offers a similarly nonchalant response to Aunt Alexandria's concerns, remarking, "What on earth could Ewell do to me, sister?"
When Bob Ewell later attacks Jem and Scout, intending to kill them, it becomes clear that Atticus severely misjudged Bob's character. Atticus's conversation with Sheriff Tate afterwards further illustrates his naiveté. Even confronted with the reality of Bob's horrifying actions, Atticus struggles to comprehend how someone could be so evil:
“I thought he got it all out of him the day he threatened me. Even if he hadn’t, I thought he’d come after me.”
“He had guts enough to pester a poor colored woman, he had guts enough to pester Judge Taylor when he thought the house was empty, so do you think he’da met you to your face in daylight?” Mr. Tate sighed.
Tate's exasperated response highlights Atticus's innocence, demonstrating that Atticus could have easily anticipated Bob's actions had he not been so naively determined to believe the best of everyone.