What Could Have Been: Originally Harper Lee wrote a book called Go Set a Watchman about an adult Scout coming to terms with life in the South as the Civil Rights Movement begins to pick steam. However, her publisher/editor was more intrigued by the childhood flashbacks and asked her to rewrite the book based on those scenes, which became To Kill a Mockingbird. Decades later, the manuscript for Go Set a Watchman was rediscovered and published.
Write Who You Know: Scout was based on Harper Lee's childhood, Atticus on her lawyer father, Jem on her four-year older brother, and Dill on her childhood friend Truman Capote. Boo Radley was based on one of her neighbors (Alfred "Son" Boleware, who was put under house arrest by his father well into adulthood after a teenage vandalism incident), and Tom Robinson was the amalgam of several cases. Ultimately everyone in the book is based off of someone from Lee's childhood. The townspeople were not amused. However, the book was Vindicated by History in Monroeville (Lee's hometown). They perform a stage version of it every year with Audience Participation for the courtroom scene: the audience is segregated as they were in the courtroom, and twelve men from the crowd are selected as the jury.
Woolseyism: The Italian title of the book and movie is 'Il Buio Oltre La Siepe', 'The Darkness Beyond The Hedge', which is a pretty poetic description of the main theme of both works; not just racism, but also fear of the unknown, whatever is in that darkness that is just beyond the hedge that borders the world we do know, like Boo Radley.
The 1962 film adaptation:
Amateur Cast: Scout and Jem were played in the film by Mary Badham and Phillip Alford, local kids from near the shooting site. Neither had any acting experience. Alford had a few TV roles later, while Badham was cast in several film and TV productions, notably as Sport Sharewood in The Twilight Zone (1959) and Willie in This Property Is Condemned, where she sings "Wish Me a Rainbow". A heavy Alabama accent prevented her from moving on to an adult acting career. John Megna (Dill) was the only kid in the cast with substantial acting experience, most of it on Broadway. He went on to do many films and TV episodes (he was the "Bonk bonk on the head!" kid from the Star Trek: The Original Series episode "Miri") before dying of AIDS at 42.
Creator-Preferred Adaptation: Harper Lee was on set for the first day of filming and was reduced to tears by how well Gregory Peck embodied Atticus Finch.
Deleted Role: Ruth White's role as Mrs Dubose was heavily cut down, because producers felt her scenes slowed the pace down.
Dyeing for Your Art: Robert Duvall stayed out of the sun for six weeks and dyed his hair blonde, for the role of Boo Radley who, according to the story, spent much of his life as a recluse.
He Also Did: The touching, distinctive piano in the opening theme music was played by John Williams, back when he was still mainly a session musician for film scores.
Hostility on the Set: Mary Badham (Scout) and Philip Alford (Jem) didn't get along while filming. She messed up nearly every take in which the family eats at the table. He didn't like eating the same meal dozens of times, so in one of the takes of the scene, in which he rolls Badham in the tire, he aimed it at an equipment truck in an attempt to hurt her. As adults however, Badham has stated that she and Alford get along fine now, and remain good friends.
Mary Badham chose to retire from films after this, so she remained as Scout in the public consciousness. Even Gregory Peck - with whom she remained close friends - continued to call her Scout as an Affectionate Nickname.
Collin Wilcox was active in the Civil Rights Movement, but after playing Mayella Ewell, she sometimes had to remind fellow activists that she was just playing a character in response to their sideways looks.
Life Imitates Art: At a couple of points in the movie, Scout, who is only just learning to read, sits on Atticus' lap to visually follow along as he reads aloud. In the book, Scout says she's been doing this since infancy and Atticus is sliding a finger under the words as he reads them to her. She doesn't remember when she started being able to read herself. Decades later, real-life educators began recommending this very technique to parents who wanted to help their youngsters learn to read.
One-Take Wonder: Atticus Finch's closing statement, in which Finch demanded the jury "do their duty", was originally planned to take several days. But Gregory Peck somehow managed to nail the speech in only one takethat alone was enough to guarantee Peck's first (and only) Best Actor Oscar.
Universal wanted Rock Hudson to play Atticus in the film, but he was deemed too young for the part. Spencer Tracy was the director and producer's first choice, but he was unavailable. James Stewart was also offered the part, reportedly second, but told the producers he believed the script was "too liberal," and feared the film would be controversial.
The play was announced in 2016 but didn't open on Broadway until two years later, and the difficult adaptation progress at one point led to a lawsuit from the estate of Harper Lee due to apparent changes to the novel that was eventually settled.
Producer Scott Rudin faced controversy after he sued community theatres who were performing a previous adaptation of To Kill a Mockingbird written by Christopher Sergel for copyright interference. After a backlash, Rudin withdrew his suits and allowed the companies to use Aaron Sorkin's script free of charge.
Greg Kinnear was slated to take over the role of Atticus Finch from Ed Harris before the COVID-19 pandemic forced Broadway to shut down.