Simon de Pury, the star auctioneer and former Sotheby's chairman, takes center screen in “The Hammer,” a documentary by Simon Wallon that world-premieres at the Zurich Film Festival.

Everyone knows Jeff Koons or Marina Abramović, but the art world has been hiding another celebrity, the film argues: de Pury, a man one nickname has followed for decades.

“He’s in the shadows but also in the spotlight. It’s precisely this contrast that fascinates me and makes him a good character for a film: someone who’s reserved and almost shy at times but then becomes the ‘Mick Jagger of auctions.’ This nickname suits him well,” says director Simon Wallon.

The film was produced by Kiss & Kill, AIG, Formapro Films, On a Whim Films, Lazy Mike Gallery and Black Square Magazine. Wallon previously directed “Bonnie,” about casting director Bonnie Timmermann, and says he was immediately drawn to de Pury’s “magnetism, knowledge of art and larger-than-life personality” — not to mention his exuberant style on the rostrum.

Wallon addresses a common suspicion head-on. “When we come from the outside, we often assume that what he does could hurt artistry or art in general. But within the art world, it’s not perceived that way at all,” he notes.

In the documentary, artists including Chloe Wise, Lou Zhenggang, Koons and Abramović sing de Pury’s praises. The film revisits his past auctions, among them a sale in Moscow that felt “like a historical event where communism and capitalism collided,” Wallon says.

As for de Pury himself, he doesn’t mind the Jagger comparisons. Not at all.

“Decades ago, [writer] Bob Colacello introduced me this way. Other monikers mentioned ‘Leonard Bernstein or [conductor] Herbert von Karajan of the auction world,’ but it’s the Mick Jagger one that stuck,” he recalls. “As an unconditional admirer of the Rolling Stones, I have, of course, done nothing to dissuade anyone from saying it.”

He does not encourage apprentice auctioneers to follow his lead. “Whenever I train young auctioneers, I tell them: ‘Don’t try to imitate anyone – be yourself.’ The style of the auctioneer I’ve most admired, Peter Wilson [the chairman of Sotheby’s from 1958 to 1980], could not have been more different from mine.”

The gavel still rattles him. “I have extreme stage fright before every single auction,” he admits.

The stakes justify the nerves. “The responsibility of any auctioneer is to obtain the highest possible price. At Sotheby’s or Phillips, an important part of their yearly [revenue] can be decided within an hour during the big evening sales. For a charity, their yearly budget can depend on it.”

He adds: “For me, every auction I conduct is the most important one I’ve ever done. Being good at the last one doesn’t mean you’ll automatically be good at the next one. It requires maximum mental and physical concentration.”

According to de Pury, Wallon’s film opens a window onto a world that isn’t easily accessible. “It also demonstrates that passion and curiosity for art ultimately bring everyone in the art world together,” he says.

Wallon found a guiding theme in his subject’s refusal to stop. “In the film, Simon says that he never stops dreaming, just like when he was a kid. And that the minute you stop dreaming, it’s the end. I couldn’t agree more,” he notes.

De Pury, after all, is also an artist, a photographer — and a DJ known as The Swiss Crocodile.

“Dreaming gives you that energy – dreaming in the sense of wanting to achieve things and believing it’s possible. The difficulty lies in keeping that up for as long as possible, and Simon has managed to keep that little flame lit through the years,” says the director. “I think that’s what gives him all that energy. He genuinely marvels at the things he sees.”

With “The Hammer,” Zurich audiences will get their first look at a figure who has spent a lifetime selling art’s biggest names — and who still gets stage fright every time he lifts the gavel.