Well, by now you've probably all read about the fact that old Atticus disappoints his grownup daughter, Jean Louise (aka "Scout") when she returns to town as a grownup and discovers that her father is a stodgy southern racist. I write about all of this here.
One of the points I make is that the character of Atticus--the one we meet in To Kill a Mockingbird--might, in fact, be the one Harper Lee meant us to remember. He was, after all, brought to life during Lee's revisions of Go Set a Watchman. This happens during the revision process sometimes. My first take on Charlotte Edwards--the main character of Charlotte's Rose--was timid. Fearful. Her journey was to discover her own bravery.
But somewhere during one of the drafts I got bored with that Charlotte and turned her into a bold girl. A feisty girl. A girl who would impulsively volunteer to carry a baby across the plains and then be stubborn enough to do it.
We'll never know how the character of Atticus Finch evolved, ultimately. And the truth is the Atticus in Watchman may well be a more realistic character given the story's time and place.