There is no hotter commodity in pop culture than Marvel Comics superheroes. They’re the powerhouse behind four hit films this year (including the top two in global box office, Disney’s $3.6 billion tandem of “Black Panther” and “Avengers: Infinity War”) and on television they’re featured in 10 live-action series spread across ABC, Fox, Netflix, FX, Hulu and Freeform as well as five more animated franchises.

Don’t expect a break during the commercials, either, where Marvel creations are the costumed pitchmen for Ford, Geico, Infiniti and Rocket Mortgage. There is one sector, however, where Marvel heroes are not soaring to new heights, one in which they struggle to find new fans — and in a wry twist, it’s in their original medium, in the pages of Marvel Comics.

Marvel comic books, which introduced the world to such characters as the Avengers, Spider-Man, the X-Men, Deadpool and Venom, is still the brand to beat in its sector — over the past decade, Marvel has locked down the No. 1 spot in its annual market share competition with rivals including DC Comics, Image and Dark Horse.

But the picture is less rosy when Marvel competes with its own past. Today’s comics sell one-tenth the numbers Marvel expected in the 1960s and 1970s glory days when comic books were cheaper than candy bars and just as easy to find at the nation’s newsstands, corner markets and drugstores.

Now, a new comic book costs $4-$6 and the only shelves they reach are at the 2,500 comic book specialty shops doing business in the U.S. and Canada — and even that number is in decline as stores lose their leases or downsize to online merchants.

There’s an even steeper challenge: For young consumers, could any comic book ever stack up against video games, smartphones and Pixar films?

All monthly comics by Marvel, DC and other leading publishers reach readers through Maryland-based Diamond Comics Distributors, which reported that in 2017 single-issue sales were down more than 10 percent, while graphic novels (which reprint the most popular multiple-issue storylines into the “trade paperback” format sold at bookstores) were down more than 9 percent.

The New York-based Marvel Comics brought its top creative talent to Comic-Con International in San Diego, the largest pop culture convention in the world. Fans heard about major new publishing directions for Captain America and the Fantastic Four as well as plans for the company’s 80th anniversary celebration in 2019.

The panel presentations put Marvel editors face to face with impassioned longtime fans who, like “Star Wars” followers, veer between fawning or furious but are never apathetic.

The diehard Marvel readership were nicknamed “True Believers” back in the 1960s when the publisher promoted itself as “the House of Ideas” and boasted a legendary staff bullpen (led by Stan Lee, Jack Kirby, Steve Ditko and John Buscema). They introduced a level of melodrama, humor and trippy cosmic mythology that instantly reinvented the staid superhero template that had been set in the FDR era by Superman, Batman and Wonder Woman over at archrival DC Comics.

Like today’s Marvel films, the energy of those 1960s comics issues won over a wider and older audience than previous superhero fare. Marvel in the 1960s energized the entire comics industry by winning over an audience that was more grown-up but now (with a fan base of collectors in their 30s), the publisher’s readership is growing old.

The monthly comics are written to appeal to longtime fans, which means they often have very little in common with the current storylines of films such as “Ant-Man and the Wasp” or TV shows such as “Legion,” “Daredevil,” “Punisher” or “Jessica Jones.”

It adds up to a frustrating disconnect, according to Heidi MacDonald, editor in chief of the Beat, a comics industry blog.

“With Marvel Comics, they’re definitely down from where they were five years ago even as the movies have gotten huge,” MacDonald said. “But over that time, they have also been No. 1 in the direct market for something like 99 percent of the time.

“The movies and, to a lesser extent, the TV shows have made Marvel a household brand name, and when you have a film that is tied to a specific storyline — like (the Fox film) ‘Logan,’ which was based on the graphic novel ‘Old Man Logan’ — there is definitely interest in that title. But when you see the brand power outside of comics the question people ask is, ‘Are they doing as much as they could with that?’ ”

Few people in Hollywood have more history with comic books adaptations than Michael Uslan, who began writing comic books in the 1970s and used that expertise as an executive producer on Tim Burton’s “Batman,” the 1989 hit that launched a new generation of superhero movies. Uslan recalled recently that top Marvel Comics executives treated him to a lavish Manhattan meal after the movie stirred fan interest in all comics and gave Marvel a hefty spike in sales.

“That was the case for years, big superhero movies brought new fans to comics, but it’s not the case now,” Uslan said. “The biggest comic book movies now have little or zero impact on the comics sales. The movies aren’t rescuing the comics; they’re replacing them. Any entertainment medium that can’t connect with new generations, doesn’t it have one foot in the grave?”

Uslan and most longtime observers agree that on paper, at least, the future of Marvel appears far smaller than its past, but that’s not a world view shared by Dan Buckley, the president of publishing for Marvel Entertainment and an industry veteran who responds to the chorus of doomsayers with a survivor’s chuckle.

“I’ve been managing over the demise of the print comic book business since 1991,” Buckley said. “That’s all anyone has talked about — how this is going to end. I find it fascinating that there’s a certain cynicism built into the beast. I’ve been fighting against it for a really long time.”

The truth, he says, is that, “it’s a pretty fabulous business to be in.”