ALL KIT LAMBERT and Chris Stamp wanted was to make a movie.

When the two decided in 1964 to make a documentary about a West London rock 'n' roll group, their fates were sealed. The band they set their sights on became the Who, and Lambert and Stamp became two of the most notorious—and ingenious—rock managers in a field crowded with the likes of Brian Epstein, Andrew Loog Oldham, and Robert Stigwood.

Lambert, in particular, is a fascinating figure, a character worthy of a movie all his own. (That movie could still be coming—Cary Elwes has been attached to direct a Lambert biopic.) The Oxford-educated son of a well-regarded classical composer, Lambert had an unconventional upbringing that bridged England's conservative upper-class aristocracy and the anything-goes flamboyance of his father's artistic peers. After finishing school, Lambert traveled to the Amazon, where natives killed one of his colleagues; upon his return to England, he worked on movies like From Russia with Love and The Guns of Navarone. Later, as the Who's producer, he urged Pete Townshend to compose something more substantial than three-minute pop songs; "A Quick One While He's Away" and Tommy were the groundbreaking results. Naturally, Lambert was a man of appetite and ego, and his life ended in a fog of drugs, rent boys, and booze at age 45.

Stamp, on the other hand, was strictly working class, the brother of renowned actor Terence Stamp and the perfect everyman foil to Lambert's upper-crust gentleman. He was as hetero as Lambert wasn't, first breaking into showbiz as a stagehand at the ballet, a position that suited him perfectly, as he could eyeball the female dancers during the performance, then ball them afterward.

The two men came together at an auspicious time and place: London in the 1960s. On the heels of the Beatles' epoch-shifting breakthrough, and as James Bond was exporting British suavity to every cinema screen on the globe, the United Kingdom's capital became a hotbed of artistic creativity, the fecundity of which remains nearly unmatched. As post-war gloom finally gave way to Carnaby Street Technicolor, an entire nation loosened its neckties and apron strings. Sex, drugs, and rock 'n' roll were the prize for many, and the pitfalls for some.

Lambert & Stamp is the brilliant, wholly absorbing documentary about both the era and the managers' partnership. It was painstakingly assembled over many years by director James D. Cooper, whose own bulldog filmmaking style works well with his subject matter. There's plenty about the Who, of course, including Lambert and Stamp's vibrant footage of the band performing in a seedy London pub, years before Monterey Pop and Woodstock. And there are the requisite Keith Moon stories, although one of the film's most powerful moments comes when Townshend and Roger Daltrey quietly discuss the troubled drummer's mental health problems. But this remains chiefly a film about the Who's two fascinating managers. Working in unlikely concert, Lambert and Stamp transformed Townshend, Daltrey, Moon, and John Entwistle ("a fucking genius," Townshend yells in one interview) from a bunch of street-fighting yobs into a multifaceted pop-art act at the height of Swinging London—an incredible feat given how volatile the relationships between the group's members were.

Massive success followed, and of course it all went to shit as the partnership dissolved in lawsuits, acrimony, and frantic grabs for cash. The documentary is insightful, sad, and moving, making particular use of a series of interviews conducted with Stamp before his death in 2012. He and the surviving members of the Who are reconciled, and they're as amazed as we are at the remarkable, weird, tragic, triumphant story of their lives.

Lambert & Stamp comes at a bountiful time for the Who's devoted. The band's studio albums have all been newly reissued on vinyl, and Mark Blake's excellent new biography, Pretend You're in a War: The Who and the Sixties, was just published a few weeks ago. Meanwhile, Daltrey and Townshend are currently touring for the band's "50th" anniversary (a number that I think must come from the release date of their first single, "I Can't Explain"). With Cooper's terrific documentary, we have more insight than ever into an incredibly mismatched group of men who made violent, impassioned, often misunderstood music.