A character from the ‘Transformer’ movie dominates a room during Comic-Con International 2016. File photo/AFP

From Peter Parker's run-in with a radioactive spider to Superman fleeing an exploding Krypton: comic book fans love a good origin story.

So when 135,000 geeks and nerds invade San Diego next week for the 50th edition of Comic-Con — the world's largest celebration of pop culture — the event's humble beginnings will be a hot topic of discussion.

The sprawling convention today draws Hollywood A-listers like Arnold Schwarzenegger, Patrick Stewart and the cast of "Game of Thrones" to its frantically hyped panels, where billion-dollar franchises are launched.

But the first iteration — the brainchild of an unemployed 36-year-old comic collector and his five teenage acolytes — drew just 100 people to a seedy hotel basement down the road in March 1970.

The "Golden State Comic-Con" was first designed as a way for fans to connect with each other and meet their heroes — the comic book creators — at a time when the genre was a million miles away from the mainstream.

A cosplayer poses for a picture at Comic Con in San Diego. File photo/AFP

"We never thought we'd be as big as we are. We never thought we'd be around in 50 years' time," David Glanzer, Comic-Con's marketing chief, said.

Star Wars to Tarantino

"They were the first people who really viewed comic books as art," added Glanzer.

Comic-Con's subsequent growth was gradual but inexorable. It increasingly looked beyond comics and catered to film and TV, as well as other genres such as sci-fi.

Oscar-winning director Frank Capra was the first genuinely mainstream star to attend. But arguably the tipping point came in 1976 when Lucasfilm's publicist sent a team bearing posters and slides to promote an upcoming "little film called Star Wars," said Glanzer.

Writer/director Francis Ford Coppola attends "Twixt" Press Line during Comic-Con 2011. File photo/AFP

The ploy to spread word of mouth about its ambitious space opera was "viral marketing before there was viral marketing," he added.

By the 90s, studios and networks were sending the "talent" itself — star-studded casts and directors — forcing the traditional media to pay attention.

Comic roots

This year San Diego will host a series of retrospective panels celebrating Comic-Con's storied past.

But for some, the exponential growth has come at a cost.

Anya Klam, 5, plays the part of BB-8 from Star Wars during Comic-Con International 2016. File photo/AFP

Comic retailers who maintained stalls at the event for decades have stopped coming, priced out by rising costs as Comic-Con has filled and spilled out from the 27-acre (11-hectare) San Diego Convention Center.

And many bemoan the fact that, in a world of Hollywood blockbusters and video games, the comic books themselves have been relegated to the back pages.

"Yeah we do get a lot of hollywood people, but entertainment now is very different to how it was in 1970," said Glanzer. "I think that's just a healthy progression and acknowledgement of art in its various different forms.

"As long as we maintain our roots in comics and other art forms, I hope we'll be okay."

Agence France-Presse