If he could go back in time and do it again, Bob Gale probably wouldn’t change much about “Back to the Future.” This 1985 science-fiction comedy, about a teenager taking a whirlwind trip to the year 1955 in a time-traveling DeLorean built by an eccentric inventor, became an endearing and endlessly quotable box-office smash.The film, which Gale wrote with its director, Robert Zemeckis, also turned into a cultural phenomenon. It bonded its stars, Michael J. Fox and Christopher Lloyd, to their quirky characters and spawned two hit sequels that its creators envisioned as a self-contained saga.When the words “The End” appeared onscreen in “Back to the Future Part III,” Gale explained in a recent interview over lunch, it was a message to audiences. “We told the story we wanted to tell,” he said. “And we’re not going to milk you guys for a substandard sequel.”But like its emblematic DeLorean, the “Back to the Future” franchise has continued to reappear in the ensuing decades, in authorized books, games and theme park rides, in cast reunions and countless pop-cultural homages.The gang’s all here: Doc Brown, Marty McFly and, at the center of some of the show’s much-anticipated stunts, a replica of the DeLorean time machine.Nina Westervelt for The New York TimesNina Westervelt for The New York TimesNina Westervelt for The New York TimesAnd now on Broadway: “Back to the Future: The Musical,” which opens Aug. 3 at the Winter Garden Theater, follows a story that will be familiar to fans of the film. Using a time machine devised by Doc Brown, Marty McFly travels to 1955, meets his parents Lorraine and George as teenagers and must help them fall in love after he disrupts the events that led to their romantic coupling.On its yearslong path to Broadway, “Back to the Future” has faced some challenges that are common to musical adaptations and others unique to this property.While the show’s creators sought actors to play the roles indelibly associated with the stars of the film and decided which of the movie’s famous scenes merited musical numbers, they were also trying to figure out how the stage could accommodate the fundamental elements of “Back to the Future” — like, say, a plutonium-powered sports car that can traverse the space-time continuum.Now this “Back to the Future” arrives on Broadway with some steep expectations: After a tryout in Manchester, England, its production at the Adelphi Theater in London’s West End won the 2022 Olivier Award for best new musical. The show also carries a heavy price tag — it is being capitalized for $23.5 million, according to a filing with the Securities and Exchange Commission.Throughout its development process, the people behind it — including several veterans of the “Back to the Future” series — tried to remain true to the spirit of the films and keep intact a story that has held up for nearly 40 years.Bob Gale, who wrote the original movie with Robert Zemeckis, said of the stage adaptation: “We didn’t want to reinvent the wheel. We just want to make the wheel smooth.”Nina Westervelt for The New York TimesAs Gale, now 72, put it: “We didn’t want to reinvent the wheel. We just want to make the wheel smooth.”But, he added, “It cannot be a slavish adaptation of the movie. Because if that’s what people want to see, they should stay home and watch the movie. Let’s use the theater for what theater can do.”Gale’s inspiration for “Back to the Future” came in 1980 after seeing a photo of his father as a teenager in an old high-school yearbook, and he has become a passionate custodian of the franchise. That role dates back to at least 1989, the year a notorious “Back to the Future” Nintendo game was released. “One of the worst games ever,” he said. “I was so horrified by that I actually gave interviews to tell people, ‘Do not buy it.’”In 2005, after Zemeckis and his wife, Leslie, attended a performance of the Broadway musical “The Producers,” the “Back to the Future” creators began to contemplate a stage adaptation of their film. They hired Alan Silvestri, who wrote the scores of the “Back to the Future” movies, to create new songs with Glen Ballard, the pop songwriter who had worked with Silvestri on Zemeckis’s 2004 film version of “The Polar Express.”Gale said that as he and Zemeckis started to meet with Broadway producers, “They said all the right things. But their agenda really was, let’s get Zemeckis and Gale off this and give it to our own people to do it.”That was something Gale said he would never allow to happen. “These characters are like my family,” he said. “You don’t sell your kids into prostitution.”Instead they enlisted the British producer Colin Ingram, whom Ballard had worked with on the musical adaptation of the film “Ghost.” They hired the highly sought-after director Jamie Lloyd, and then parted ways with him in 2014. “The creative differences and the chemistry just didn’t work,” Ingram said. (Through a press representative, Lloyd confirmed that his departure was a mutual decision over creative differences but declined to comment further.)Behind the scenes: The show’s designer, Tim Hatley, was charged with evoking the spirit of the beloved film.Nina Westervelt for The New York TimesNina Westervelt for The New York TimesNina Westervelt for The New York TimesUpon regrouping, the creators met with John Rando, who had directed “Urinetown” and “The Wedding Singer.” Rando said that after their initial meeting, “I grabbed Bob by the shoulders, looked him in the eye and said, ‘Bob, I love these characters. And I promise you I’m going to take really good care of them.’” Within a half-hour Rando said he got the call that he was hired.In conceiving “Back to the Future” for the stage, Gale said certain signature moments from the movie could never work: No scene of Doc Brown being attacked by disgruntled Libyan terrorists. (Now Marty speeds off in the DeLorean after Doc is overcome by radiation poisoning.) No set piece in which Marty races through the town square on a skateboard while the meathead bully Biff pursues him in a convertible. (Now the chase occurs on foot at school.) No pet dog named Einstein for Doc Brown. (Sorry, there’s just no dog.)A scene from the film where Biff is stopped before he can assault Lorraine remains in the show, though Gale acknowledged that this moment was “edgy.”“We want the audience to feel the jeopardy, and they do,” Gale said, adding that there were many elements from “Back to the Future” that might not withstand scrutiny if the film were being pitched today.Yet other familiar scenes presented opportunities for invention. Silvestri said he and Ballard were not given an exacting road map for where songs should go or what they should sound like. “We just kept trying to find our way,” Silvestri said. “It’s calling for a song here. It’s demanding music there.”The composers felt there had to be a rousing opening number to establish the show’s popped-collared, neon-colored version of the year 1985 and use the “Back to the Future” fanfare, and that became the song “It’s Only a Matter of Time.” There also had to be a love song for the smitten young Lorraine to serenade the enigmatic visitor she doesn’t realize is her own son, which yielded the doo-wop pastiche “Pretty Baby.”The curtain has lifted on “Back to the Future: The Musical,” but the creators of the franchise said they have no intention of pursuing more films.Nina Westervelt for The New York TimesThroughout the show’s development, there was a consensus that high-tech engineering and video projections would help recreate complicated scenes like Doc Brown’s perilous ascent of the Hill Valley clock tower during a fateful lightning storm.But Rando said he entrusted these elements to the show’s designer, Tim Hatley, and his production colleagues while the book, songs and performances were being nailed down.“They would keep asking me, ‘Hey, let’s talk about the clock tower sequence,’” Rando explained. “And I said, ‘Not until we get this musical right.’ And we would do readings and readings, and then finally there was a moment where we’re like, OK, now we can do it.”The actor Roger Bart, who has starred in musical comedies like “The Producers” and “Young Frankenstein,” was an early candidate to play Doc Brown. He landed the role with the help of a video audition in which he wore a lampshade on his head (to mimic a mind-reading device Brown uses) and sung the Talking Heads song “Once in a Lifetime.”Though Christopher Lloyd is associated with the Doc Brown character, Bart said he felt it was not his job to copy that performance.“I’m 60,” Bart said. “There’s a certain point where I have to go, I know I’m entertaining. I’ve been in front of enough audiences to know that. If you really get bogged down with that thinking, you’re going to paralyze yourself.”The best way to play Doc Brown, Bart said, is to honor the spirit of Lloyd’s performances, “which is to create the idea that anything can happen at any moment, by being unusual in your choices.”Casey Likes joined the show as Marty for its Broadway run, after making his Broadway debut last year in “Almost Famous.” He said that his mother often compared him to Michael J. Fox when he was growing up. (The actor, who is 21, was born 16 years after “Back to the Future” was released in theaters.)At his audition, Likes said, “I wanted to convey something that was reminiscent of Michael but not an impression.”He added, “I went with the kind of vocal inflections that he had done, while trying to deliver the bright-eyed, somewhere between cool and dorky thing that he did. And I guess it worked.”As the curtain goes up on this “Back to the Future,” its creators are hopeful that it is a faithful representation of the franchise — one that they say they have no intention of continuing cinematically. As Gale put it, “We don’t need ‘Back to the Future 18.’”For its stars, their day-to-day hopes are more focused on steeling their courage when they step into the show’s mechanical DeLorean and trusting it will execute its stunts consistently.With a wry chuckle, Bart said he’d rather not have a day of work that ends with anyone “being sent to the hospital while the stage managers say, ‘I’m so sorry, I can’t believe I called that wrong,’ and you go, ‘Oh, it’s OK, I have insurance, it’s all good.’ I don’t ever want to have that conversation.” More