Stanley Kubrick had many compulsions, like his famous fear of flying, and one of them was privacy. Considering what a unique superstar of a filmmaker he was, he succeeded in leading more or less his entire life outside the media fishbowl. That’s why after a certain point (around the post-“2001” late ’60s, when he was still transitioning from major Hollywood director to monomaniacal living legend), there is so little up-close coverage of who he was, on and off the set. Recently, though, a lot of Kubrickiana has begun to seep out of the woodwork, some of it gathered into termite-art documentaries like “Stanley Kubrick’s Boxes” (about his vast collection of memorabilia) or “S Is for Stanley” (about Kubrick’s relationship with his long-time Italian chauffeur and personal assistant).

“Filmworker” is the best of these films yet. Directed, shot, and edited by Tony Zierra, it’s a portrait of Kubrick’s right-hand man, who devoted himself to the religion of all things Kubrick, but beyond that the film has a special value: It ushers you into the world of how Kubrick put his movies together.

Fittingly, it’s the story of an obsession. In the early 1970s, Leon Vitali was a pouty young British actor who was just handsome enough, in a dyspeptic blond Mick Jagger way, to be a popular presence on British television. He had a thriving career, and was even a bit of a teen idol, when Kubrick cast him in “Barry Lyndon” as Lord Bullingdon, the stepson of Barry who seethes in hidden agony at the scoundrel who has married his mother and scandalized his family. Bullingdon becomes Barry’s antagonist, and it’s part of the acerbic moral flavor of “Barry Lyndon” that Barry is the film’s hero, but we’re basically on Bullingdon’s side.

Vitali describes meeting Kubrick for the first time, shaking his hand and feeling an almost menschy warmth. That feeling never went away, but other feelings — like fear and intimidation — soon joined it. Vitali, like almost any actor, leapt at the chance to work with Kubrick, and he got an early taste of what that was like when the director shot endless retakes of the scene in which Ryan O’Neal’s Barry beats the holy crap out of Bullingdon. Kubrick kept telling O’Neal, “You’re not hitting him hard enough.” But Vitali didn’t mind; even before that, he had joined the cult of Kubrick. In “Filmworker,” he tells a story about going to see “A Clockwork Orange” and getting so caught up in its plastic operatic sadistic theatrical glory that when the movie was over, he turned to the friend he’d come with and said, “I want to work for that man.”

As the “Barry Lyndon” shoot was ending, Vitali asked Kubrick about the possibility, and Kubrick told him to go out and get some experience. So he did, sitting in on the editing of a “Frankenstein” movie he was starring in. When he reached out to Kubrick again, Stanley had an assignment for him: He asked Vitali to go to the U.S. and cast the role of Danny Torrance in “The Shining.”

Vitali, who is now in his late sixties, has the weatherbeaten face, scraggly hair tucked under a pirate’s bandana, and guttersnipe British accent of an aging ’70s rock & roll manager. He took his first assignment from Kubrick and ran with it, organizing an audition for the role of Danny that encompassed thousands of kids. It was Vitali himself who discovered Danny Lloyd, and he wound up forging a close protective relationship with him. Right away, we learn something important (and rather counterintuitive) about Kubrick: For such an infamous control freak, he could be quite a delegator. Vitali also discovered the “Arbus twins” (who weren’t in the script), and he wound up on the set of “The Shining,” where his job consisted of doing anything Kubrick asked. He went out and took photographs of hotel lobbies, and since “One of Stanley’s mantras was you had to write everything down,” he wrote everything down.

As Vitali describes it, working for Stanley Kubrick was like a cinéaste version of “The Devil Wears Prada.” He was never not on call, because he constantly had to juggle matters outside the immediate shoot — like Kubrick’s compulsive tracking of whatever prints of his films were being shown at any given moment anywhere in the world, not to mention dubbings and translations. Vitali served as gofer, driver, dialogue coach, and liaison between Kubrick and the Warner Bros. studio executives. The work could be arbitrary and relentless, but the job became a mission, and that was the source of Vitali’s bond with Kubrick. Stanley trusted his devotion.

“Filmworker” has great stories from Matthew Modine, who describes Vitali on the set of “Full Metal Jacket” as being a little like Frankenstein’s groveling helper-slave Igor, and from R. Lee Ermey, who recalls how he used Vitali to stalk and capture the role of Gunnery Sergeant Hartman. The movie also features a great deal of previously unseen photographs and footage of Kubrick on the sets of all his films, and just watching him tells you a lot.

Kubrick comes off as a forceful, shaggy, often smiling aesthete-dictator. He would fire an actor for not knowing his lines, and his method of doing take after take was, to him, no more heartless or demanding than a painter going over a section he’d already painted; it was all just part of the process. In a way, the film demystifies Kubrick, but it also reveals what a politician he was. He’s described as a chameleon of coldness and camaraderie, manipulation and sincerity who allowed each person he interacted with to think that they were seeing “the real Stanley.”

“Filmworker” is a brisk, compelling movie that’s pure candy for Kubrick buffs, yet there are oddities about it. Its central conceit is that Leon Vitali “gave up fame and fortune” to go to work for Stanley Kubrick, yet it’s not as if this was Ryan Gosling committing himself to a monastery; there’s every chance that Vitali, had he continued on as an actor, would have wound up doing bad British sitcoms. What’s more, the course of his life remains a little vague. Because he fastened onto Kubrick just as Kubrick began to take eccentrically long canyons of time in between projects, Vitali worked for him for two decades…but that meant doing just three films (“The Shining,” “Full Metal Jacket,” and “Eyes Wide Shut”).

Yet the wear and tear those shoots took on him was all too real. By the time of “Eyes Wide Shut,” he was skin and bones, often working literally 24 hours a day. The Vitali we see in the movie has the grizzled, shell-shocked survivor’s grace of a true believer with a touch of PTSD. He always listed his occupation as “filmworker,” because he didn’t know what else to call himself. He didn’t have one job — he had 100. He did everything at once. In exchange, he got to bask in the light of a man who directed each movie like God staging the world.