Harper Lee, the Pulitzer Prize-winning author of the American literary classic To Kill a Mockingbird, has died at age 89.

Lee's death on Friday was confirmed by the city clerk in her hometown of Monroeville, Ala., and by her publisher, HarperCollins. No additional details were given.

Though it was her sole book for most of her life, To Kill a Mockingbird — published in 1960 — instantly lifted Lee to the status of American literary icon with its tale of racial injustice in 1930s Alabama, and a heroic lawyer defending a black man falsely accused of rape.

"The world knows Harper Lee was a brilliant writer but what many don't know is that she was an extraordinary woman of great joyfulness, humility and kindness. She lived her life the way she wanted to — in private — surrounded by books and the people who loved her," Michael Morrison, head of the HarperCollins U.S. general books group, said in a statement.

Estimated to have sold more than 40 million copies worldwide since its initial publication, To Kill a Mockingbird is considered among the most widely read American novels of the 20th century.

Drawn from childhood experiences

Born Nelle Harper Lee on April 28, 1926, in Monroeville, Lee was the youngest of four children. After attending the University of Alabama, she moved to New York, where she worked as an airline reservation clerk while pursuing a writing career in her spare time.

Harper Lee

Harper Lee, seen in 1963, won the Pulitzer Prize for her 1960 classic To Kill a Mockingbird. A sequel entitled Go Set a Watchman, her second book, was released in 2015. (File/AP Photo)

By the late 1950s, she had a manuscript ready to send out to publishers. Tay Hohoff of J.B. Lippincott Company eventually helped her shape the rough drafts into To Kill a Mockingbird, which was published in July 1960.

The novel drew in part from her experiences as the youngest daughter of lawyer Amasa Coleman Lee, who had also served in the Alabama House of Representatives.

It's believed she based the novel's famed crusader, Atticus Finch (the surname taken from her mother Frances's maiden name), on her father, who died in 1962.

The author herself was a tomboy, like her book's young narrator Scout, and she also wrote in a character to depict her childhood friend Truman Persons (who eventually grew up to take on the mantle Truman Capote). In turn, Capote used Lee as a model for a character in his first novel, Other Voices, Other Rooms

Instant critical, commercial success

"It was like being hit over the head and knocked cold," Lee said of her novel's immediate success in a 1964 interview, when she still talked to the media.

"I didn't expect the book to sell in the first place. I was hoping for a quick and merciful death at the hands of reviewers, but at the same time I sort of hoped that maybe someone would like it enough to give me encouragement."

To Kill a Mockingbird was an instant bestseller that earned Lee a Pulitzer the year after it was published.

It also quickly spawned a 1962 film adaptation that itself became an American classic, winning multiple Oscars. Atticus Finch became one of film star Gregory Peck's most indelible performances. The role also led to a longtime friendship between Lee and the actor, whose grandson is named Harper, after the noted author.

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Gregory Peck, foreground left, and Brock Peters, right, appear in a scene from classic 1962 film To Kill a Mockingbird. (Universal Studios Home Entertainment/Associated Press)

After Mockingbird, Lee travelled with Capote to Kansas to aid in his research for a new story that eventually became his 1966 bestseller In Cold Blood

Beginning in the late 1960s, Lee began to turn down interviews and withdrew from interactions with the press, remaining intensely private but active in her hometown, periodically offering vague responses when asked about a follow to her famed first novel.

The residents of Monroeville, which inspired the fictional town of Maycomb in Mockingbird, fiercely protected her privacy and carefully celebrated the legacy of Lee and her novel over the years. 

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An Atticus Finch impersonator is seen entertaining Harper Lee and To Kill a Mockingbird fans in Monroeville, Ala., in 2015. The author's hometown fiercely defended her privacy and carefully celebrated her work since the 1960s. (Brynn Anderson/Associated Press)

Late-life sequel (or prequel?)

To much surprise and controversy, a Mockingbird sequel, Go Set a Watchman, was announced in early 2015 and released to great fanfare in July. 

Despite mixed reviews from critics, many who dismissed it as a seemingly rough draft for To Kill a Mockingbird, and readers who lamented the new book's portrayal of the beloved Atticus Finch as an aging racist, Go Set a Watchman sold 1.1 million copies in the U.S. and Canada in its first week.

Controversy swirled around whether Lee, who suffered a serious stroke in 2007 and was reportedly in frail health, was able to give consent for the publication of the new book. Some questioned the timing of the "discovery" of the manuscript, which occurred shortly after the death of her eldest sister and longtime guardian, Alice.

Through a lawyer, Lee stated she was "happy as hell" to see Watchman published. 

Lee has been portrayed in both film and television, most prominently by Catherine Keener in the 2005 film Capote and Sandra Bullock in the 2006 film Infamous

OSCAR NOMINATIONS

Catherine Keener, right, portrayed Harper Lee in the film Capote, which starred Philip Seymour Hoffman as Truman Capote. (Attila Doroy/Sony Pictures Classics, AP)

Earlier this month, it was announced that a new stage adaptation of To Kill a Mockingbird, written by Aaron Sorkin, will run on Broadway during the 2017-18 season.

A 2007 recipient of the Presidential Medal of Freedom, the highest civilian honour in the U.S., Lee has also won the National Medal of Arts, countless honorary degrees and other literary prizes.

Lee has no immediate survivors. She never married and was predeceased by her elder siblings Edwin, Louise and Alice, the highly respected, longtime lawyer who died in November 2014 at age 103. 

Funeral services have not yet been announced.

With files from The Associated Press