Who is Valentino Garavani? To those who know fashion, the answer is obvious: He is the legendary Italian designer behind the Valentino line of hand-stitched dresses favored by two generations of the celebrity elite, from Jackie Onassis to Jennifer Lopez.

Yet, as Matt Tyrnauer’s absorbing new documentary suggests, Valentino, who will turn 77 in May, is hardly sated by his 45-year reign at the forefront of his industry. He is restless, perpetually dissatisfied and capable of finding even his greatest successes inadequate.

To hear him tell it, Valentino knows what women want – they want to be beautiful, and he has dedicated his life to helping them get there. But after four-plus decades in the business, he has reached the end of the line. His empire targeted for corporate takeover as rumors of his abdication abound, Valentino, deeply tanned and almost comically difficult, seems ready to step aside. Giancarlo Giammetti, his longtime partner in business and in life, senses this, and prepares an epic farewell bash at no less than the Roman Colosseum.

The Last Emperor focuses on the final two years of Valentino’s tenure at the company he and Giammetti built – Valentino left in 2007, with his savvy business manager and lone confidant following several months later – and if Tyrnauer’s documentary seems to capture the end of an era, there’s a reason. “You and I are the only ones left,” German designer Karl Lagerfeld tells Valentino on the eve of his retirement. “The rest is crap.”

Whether Valentino is ready to enjoy his final days of empire, much less the extravagantly choreographed spectacle of his farewell party – he worries that it looks like Cirque du Soleil – is another story entirely.

He seems a hard man to know, a demanding diva reluctant to thank his underlings and peers, who slave to accommodate his every whim. Yet Valentino seems not so much thoughtless or cruel as hopelessly distracted by the imperfection he senses around him. He demands beauty, but one begins to wonder how much he can appreciate it.

One thing he doesn’t appreciate is being filmed. Valentino loses his calculated cool on several occasions, demanding that the cameras be shut off to grant him a moment of privacy, often to consult with Giammetti. Even then, he seems less tyrannical than a man unsettled and used to having his way. He carries himself, as the title implies, like royalty, an emperor who’s hardly wanting for clothes. But if his reputation, his private jet, his yacht or his five adorable pugs give him the satisfaction he seems to have earned, he hides it remarkably well.

Valentino: The Last Emperor opens Friday, April 3, at the Embarcadero Center Cinemas in San Francisco.