With all the debate brewing over the origins of Harper Lee’s novel “Go Set a Watchman,” the biggest bombshell turned out to be an explosive character revelation that no one saw coming.

Atticus Finch, the crusading lawyer of “To Kill a Mockingbird,” whose principled fight against racism and inequality inspired generations of readers, is depicted in “Watchman” as an aging racist who once attended a Ku Klux Klan meeting, holds negative views about African-Americans and denounces desegregation efforts. “Do you want Negroes by the carload in our schools and churches and theaters? Do you want them in our world?” Atticus asks his grown daughter, Jean Louise, in “Watchman.”

The stunning revelation will probably alter readers’ view of Ms. Lee’s cherished first novel and could reshape her legacy, which until now has hinged entirely on the outsize success of her 1960 novel “Mockingbird,” a beloved book that has sold more than 40 million copies globally and occupies a unique place in our literary culture.

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It is also certain to spur debate about the character of Atticus, and his moral integrity in “Mockingbird” — a staple of high school curriculums around the country — that made him a cultural icon whose influence transcended literature, inspiring generations of lawyers, teachers and social workers. “Whether you’ve read the novel or seen the film, there’s this image you have of Atticus as a hero, and this brings him down a peg,” said Adam Bergstein, a high school English teacher in Queens who teaches “Mockingbird” to 10th and 11th graders. “How do you take this guy who everybody looked up to for the last 50-plus years, and now he’s a more flawed individual?”

The new version of Atticus, 72, suffering from arthritis and stubbornly resistant to social change, stands in sharp contrast to the gentle scholar in “Mockingbird,” who tells Scout, when explaining why he has gone out on a limb to defend a black man, that “I do my best to love everybody.”

In “Watchman,” which comes out on July 14, Atticus chides Scout for her idealistic views about racial equality: “The Negroes down here are still in their childhood as a people.”

The revelation comes at a moment when issues of racism, inequality and the persecution of minorities in the United States are again at the forefront of the news. Last week, the South Carolina legislature voted to remove the Confederate battle flag from its statehouse grounds, after days of emotional debate. Protests have erupted around the country following police shootings of unarmed black men.

“Watchman,” which was completed in 1957, is landing in the middle of the debate, like a literary artifact out of a time capsule from a period when the country was divided over many of the same issues.

“We could turn this into a plus in our national conversation about racism and the Confederate Flag. It turns out that Atticus is no saint, as none of us are, but a man with prejudices,” said Charles J. Shields, author of “Mockingbird: A Portrait of Harper Lee.”

Some writers and literary critics see added value in a more complex, and flawed, version of Atticus. If “Mockingbird” sugarcoats racial divisions by depicting a white man as the model for justice in an unjust world, then “Watchman” may be like bitter medicine that more accurately reflects the times.

“If Atticus Finch is not quite the plaster saint that he is in ‘To Kill a Mockingbird,’ there could be something rich and fascinating about that,” said Thomas Mallon, a novelist and critic, who had read only the published excerpt from “Watchman.” “The moral certainties in ‘To Kill a Mockingbird’ are apparent from the first page, and in that sense, I don’t think it’s a great novel that deals with the tormenting questions of race in America, but maybe this new one is, if it’s more nuanced.”

It is unclear why Ms. Lee set aside “Watchman” — a blunt and unsparing look at a young woman’s disillusionment at the racism that permeates her hometown and her family — to write “Mockingbird,” a more palatable coming-of-age tale. Narrated by a charming and observant child, “Mockingbird” features characters that fall neatly into camps of heroes and villains; Gregory Peck’s portrayal of Atticus in the 1962 film is an enduring symbol of a righteous lawyer and model parent.

Was the original manuscript too politically explosive for the period — too sharp a reflection of the civil rights battles brewing at the time? Since Ms. Lee’s original editor, Tay Hohoff, died in 1974, and Ms. Lee has shunned interviews for decades, the question will probably remain unanswered, though there no doubt will be countless term papers and scholarly essays devoted to the subject for years to come.

“ ‘Go Set a Watchman’ is much more forcefully about civil rights. It’s much more political, but that tells us what was in front of Harper Lee’s brain at the time,” said Mary Murphy, a filmmaker who recently released a new version of “Hey, Boo,” her documentary about Harper Lee. When she submitted the novel nearly 60 years ago, Ms. Lee was told to rewrite the book from young Scout’s perspective, and to turn it into a coming-of-age story. “My editor, who was taken by the flashbacks to Scout’s childhood, persuaded me to write a novel from the point of view of the young Scout. I was a first-time writer, so I did as I was told,” Ms. Lee said in a statement that was released by her publisher in February.

Ms. Lee wrote the novel in the mid-1950s, when, like Jean Louise, she was living in New York and occasionally traveling home to Alabama to visit her aging father, the lawyer A. C. Lee, who is commonly cited as the model for Atticus in “Mockingbird.” In letters she wrote at the time to a friend in New York, she describes feeling unmoored by his physical decline and impending death (“I found myself staring at his handsome old face, and a sudden wave of panic flashed through me”).

She also recounts feeling like an outsider in her hometown because of her stance on civil rights: “I don’t trust myself to keep my mouth shut if I feel moved to express myself, thereon it will get out all over Monroeville that I am a member of the N.A.A.C.P., which, God forbid. They already suspect this to be a fact anyway.”

While A. C. Lee was moderate by the standards of the times, he supported states’ rights and held segregationist views, according to Mr. Shields. Later, after the publication of “Mockingbird” in 1960, his views softened, and he started campaigning for redistricting in the county to protect disenfranchised African-American voters, Mr. Shields said.

As the first reviews of the novel were published on Friday, some “Mockingbird” fans were so disheartened by the revelation that they said they were reluctant to read the new book. On Twitter, Jamie Harding, who lives in Alabama, likened learning out about Atticus’s dark side to “finding out Santa Claus beats his reindeer.”

Ms. Lee’s publisher, HarperCollins, said there was never a discussion of toning down Atticus’s racist remarks to preserve his moral image.

“Harper Lee wanted to have the novel published exactly as it was written, without editorial intervention,” Jonathan Burnham, the publisher of the HarperCollins imprint Harper, wrote in an email message. “By confronting these challenging and complex issues at the height of the Civil Rights movement, the young Harper Lee demonstrated an honesty and bravery that makes this work both a powerful document of its time and a compelling piece of literature.”

Still, the character of Atticus had an impact that transcended literature in many ways, and many will mourn the loss of a cultural icon. In the last decade or so, nearly 6,700 babies were named Atticus, according to the Social Security name database.

Karla FC Holloway, a professor of English and law at Duke University who teaches a class on law, race and literature, said that the new version of Atticus may lead people to reread “Mockingbird” more closely. “It will force an interesting conversation about — if this is really Atticus — what have our own desires done to the character, and what is the literary truth?” Ms. Holloway said. “This is who we want to be as a country, but this is not who Atticus was.”