When the production designer John Myhre read the script for Bryan Singer’s original “X-Men” nearly 20 years ago, the first thing he did was draw a sketch on the back. It showed a room built by the telepath Charles Xavier, fit with a device that amplified his abilities by allowing him to locate fellow mutants across the globe.

“I drew a little head — just a circle,” Myhre recalls. “Then I went, ‘If the room helps to control it, it should always be the same distance away from his head.’ So I drew a bigger circle around that. Then I drew the wheelchair, and a ramp out from the doorway. And that became Cerebro.”

This was long before today’s superhero-saturated landscape. Beyond the then-dormant “Superman” and “Batman” franchises, there wasn’t a lot to point the way when it came to lifting the world of a comic book off the page and onto the screen. But with Myhre’s doodle, a grounded new direction for the genre took shape.

Indeed, terms like “grounded” and “reality” frequently come up when talking to key members of Singer’s crew. “Bryan wants clothes that function and are based in reality,” says Louise Mingenbach, the costume designer on Singer’s latest opus, “X-Men: Apocalypse.” Adds DP Newton Thomas Sigel, “Bryan’s aesthetic is very much one of realism and real-world logic.”

Both have worked with Singer on each of the four “X-Men” films he’s directed. (Myhre returned for “Days of Future Past,” in 2014.)

“Bryan wasn’t a comic-book geek as a child,” Sigel says. “He brought a modern filmmaker’s sensibility and storytelling. That led to a fresh way of doing a comic book.”

Back in 2000, Singer’s use of realism was far removed from, say, the circus-like atmosphere of Warner Bros.’ “Batman” series. And it would still be five years before Christopher Nolan’s hyper-realistic take on that character would build an aesthetic rally cry for DC Comics.

But more than aesthetics, Singer was interested in the corollary between Professor X and Magneto and luminaries of the 1960s Civil Rights movement like Martin Luther King Jr. and Malcolm X. “My goal,” Singer says, “was to bring it to an audience in a more believable and serious way, opening it in the concentration camp, having Wolverine — who is cynical and doesn’t understand the X-Men — be the eye of the audience.”

Mingenbach recalls wrestling with all of this early on. “Bryan kept going back to, ‘This has to work; this has to look like they can walk down the street and not be made fun of,’” she says. “So we went into that protective motorcycle look from there. They hung together as a gang, but they had individuality. Theoretically, they could blend in.”

Myhre’s designs, meanwhile, often took their leads from the actors. For example, Myhre thought Patrick Stewart, refined, elegant gentleman that he is, would carry that quality through the bowels of Xavier’s School for Gifted Children, where the X-Men’s militaristic elements resided. He conceived a sophisticated, clean look — straight lines and a cool blue palette.

That look has carried through the franchise, and Myhre says he’s taken great pride in seeing the concept honored by other production designers such as Guy Hendrix Dyas (“Inception”) and Grant Major (the latest “X-Men,” plus three “Lord of the Rings” films).

They’ve had room to play along the way, particularly on “Apocalypse,” which takes place in the 1980s and folds a neo-Egyptian theme into the mix, with the addition of the eponymous villain.

“I had to do a lot of research on the Egyptian world, because ‘Apocalypse’ is from a very early phase,” Major says. “I had to recognize what period it was from and what the architectural styles were at that time. It was a big learning phase.”

Mingenbach, meanwhile, was tasked with outfitting actor Oscar Isaac as one of the X-Men’s most striking and recognizable foes.

“Basically, the silhouette, his cowl, his collar — these things that read ‘Apocalypse’ — were important,” she says. “Then, of course, you embellish it and give it texture. Comic books are great for shape, so we tried to incorporate some of those iconic shapes that would resonate with the fans.”

The result, Singer says, might hew closer to a “comic-book aesthetic” than any other entry in the franchise to date, but not without his baked-in philosophies.

“I think ‘Apocalypse’ is the closest I’ve ever gotten to the palette of the comic, but I did it very pragmatically,” he says. “I signed the deal to do ‘X-Men’ in 1996, so I’ve been involved in this universe for 20 years. I take great care, and I take it very seriously.”