But in Go Set a Watchman, set 20 years later, the narrator Scout, his now adult daughter, is horrified when she returns to find her father spewing racist tirades and attending protest meetings by local whites fighting federal de-segregation.
He delivers observations such as: "The Negroes down here are still in their childhood as a people." And he asks his daughter: "Do you want Negroes by the carload in our schools and churches and theatres? Do you want them in our world?
"Do you want your children going to a school that's been dragged down to accommodate Negro children?"
Go Set a Watchman will be published on Tuesday in what is widely described as the publishing event of the decade. But some major US publications, including The New York Times and the Wall Street Journal, published their reviews on Friday night.
And the revelation that Finch is an unapologetic racist who defends segregation proved an inevitable bombshell on social media.
In the New York Times, chief reviewer Michiko Kakutani writes: "Go Set a Watchman is a distressing book, one that delivers a startling rebuttal to the shining idealism of To Kill a Mockingbird. This story is of the toppling of idols; its major theme is disillusion.
"How could the saintly Atticus - described in early sections of the book in much the same terms as he is in "Mockingbird" - suddenly emerge as a bigot? The reader, like Scout, cannot help but end feeling baffled and distressed."
Although Go Set a Watchman is set in the mid-1950s, Lee wrote it before Mockingbird, submitting the draft to a publisher in 1957. Her agent persuaded her to re-draft the work and she came back with To Kill a Mockingbird.
So her new novel actually represents her original portrayal of life in the fictional Alabama town of Maycomb, a thinly-veiled version of her real-life home town of Monroeville.
It hence seems to represent a much more critical and unvarnished depiction of the town where she now lives in a nursing home, aged 89. The searing indictment of Maycomb may indeed be an unwelcome portrait for locals who have been preparing to celebrate Tuesday's publication.
Many residents believed that Lee, a frail figure rarely seen in public, never wanted any more of her writings to be published, at least in her lifetime, and suspected that she was manipulated by her lawyer.
For them and for devotees across the world, the new book may be challenging reading.
"One of the emotional through-lines in both 'Mockingbird' and 'Watchman' is a plea for empathy - as Atticus puts it in 'Mockingbird' to Scout: 'You never really understand a person until you consider things from his point of view'," writes Kakutani.
"The difference is 'Mockingbird' suggested that we should have compassion for outsiders...while 'Watchman' asks us to have understanding for a bigot named Atticus."
