Robin Kwok may look like an unassuming shop owner, but he's actually humanity's best hope for destroying Godzilla.

Safely locked behind glass in the back corner of the Heroes Club, Kwok watches over the Oxygen Destroyer, an ultimate weapon that's 2 feet long and looks like the silver core of a reactor. Back in 1954, it was the only way to kill the original Godzilla. Only five of these life-like reproductions were ever made. This one sells for $13,998.

"For die-hard Godzilla fans, this is the holy grail," says Kwok.

Kwok, 54, has run the Heroes Club on Clement Street since 1990, after three years in a previous location. Technically, it could be called a toy shop, as it does sell some cheap $10 Godzilla figures, but the dozens of hand-painted stormtroopers, zombies and monsters lining the walls are closer to fine art than playthings.

Kwok builds and paints most of the models in a cramped workshop in the back of the store. Tiny paint bottles and half-finished models lay everywhere, including a 4-foot-long prop spaceship from Disney's Space Mountain, complete with dangling fiber optic cables. His tools haven't changed much since his studies at the San Francisco Academy of Art, the highest tech in his workspace is an old airbrush. He makes some models from scratch, others he assembles from limited edition resin kits. Each sculpture takes months to finish and sells for hundreds of dollars.

These days, 80 percent of his buyers are collectors from other countries, but there was one particular San Francisco local who was a big fan: the late Robin Williams.

RELATED: Memories of Robin Williams

"I met Mr. Williams in '87, when I first opened. Over time, we became friends. He lived close by to the shop, on Lake Street, so he would come here in his spare time," says Kwok. The pair bonded while they were both going through divorces, and kept in touch over the years, speaking on the phone on the day before Williams' death. Kwok keeps a pristine binder of memories from their relationship, including personal letters, magazine clippings featuring photos of Williams in the shop, and a signed receipt for a $1,200 purchase (see photos of them above in the slideshow).

While most of Kwok's work revolves around iconic sci-fi and horror franchises, Williams was more interested in Asian characters and military figures. In a 2018 Sotheby's auction of his possessions, a large-scale model tank sold for $875. In a series of now-deleted Twitter posts, his daughter Zelda asked fans for help identifying some parts of his collection, which she said included thousands of figurines.

Zelda Williams, via Twitter

As a housewarming gift, Kwok crafted Williams an original piece inspired by the 1928 film, "The Man Who Laughs." The film is obscure, but the character is immediately recognizable. Sitting on an antique chair, he wears a tattered pink and orange suit, white face paint, and a macabre red lipstick smile while holding a shotgun. It's clearly the early inspiration for the Batman villain the Joker.

Although the shop does have other celebrity clients (Nicolas Cage, Kirk Hammett of Metallica, Guillermo del Toro) and a healthy stream of walk-in window shoppers, today most of their sales take place online. To adjust to the shifting retail landscape, Heroes Club built a strong web presence, including a YouTube channel called Art of Toys that shows the meticulous detailing in pieces like Peach Blossom Island. Each eyelash on the woman's face was painted and attached individually, a grueling task that took five hours.

Adapting to changing tastes has also been a challenge for the shop. Customers enjoy characters from contemporary video games, and many franchises, like Alien, continue to produce films, but most of the stock showcases vintage properties. Kwok chalks this up to more than just nostalgia, but a change in movie-making style.

"The new 'Avengers' is visually entertaining, but once you walk out of the theater, you probably forget what it was about. In an older movie like 'Exorcist,' they don't have much budget or CG graphics, so the director has to spend more time to create the atmosphere. Those details imprint in your memory," he says.

An example of that concept hangs near the entrance to the shop: a screaming face from the "Exorcist" that only flashed across the screen for one second, but still haunts fans to this day. It's these types of details that excite Kwok the most — obscure references with such resonance they deserve to be re-created by a craftsman who'll spend hours just airbrushing eyelashes.

As for the future of the shop, Kwok admits business isn't what it used to be. He's not officially the last toy shop in San Francisco, but laments the fact that most of the others have closed. Still, he's not discouraged, and plans to continue honing his craft in the studio every day.

"I'll retire the day I can't paint anymore," he says.

Click through the slideshow for more photos of stormtrooper sculptures, the artist's workshop and a personal letter from Robin Williams

Dan Gentile is an SFGATE digital editor. Email: dan.gentile@sfgate.com | Twitter: Dannosphere