Chris Stamp and Kit Lambert, without whom Pete Townshend might never have smashed a guitar.

All Kit Lambert and Chris Stamp wanted was to make a movie.

The fate of this pair of would-be impresarios was sealed in 1964, when they decided to make a documentary about a West London rock 'n' roll group. Thanks largely to their intervention, 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. With the release of Lambert & Stamp, a brilliant, wholly absorbing documentary about the managers' partnership and the era that fed and was fed by it, the circle is complete.

Lambert, in particular, is a fascinating figure, well worthy of a movie of his own. (Which could be in the offing—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 aristocracy and the flamboyance of his father's artistic peers. After finishing his studies, he traveled to the Amazon, where a member of his team was killed by natives. Upon his return to England, he worked at Shepperton Studios, on big British productions like From Russia with Love and The Guns of Navarone. Later, as the Who's producer and manager, he urged Pete Townshend to push beyond the limits of three-minute pop singles and compose something more ambitious; "A Quick One, While He's Away" and later Tommy were the groundbreaking results. Naturally, Lambert was a man of appetite and ego, and his life ended at age 45 in a fog of booze, drugs, and rent boys.

Stamp, on the other hand, was strictly working-class, the brother of renowned actor Terence Stamp and a 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 dancers during the performance and then court them afterward.

The men came together at an auspicious time and place: London in the early 1960s, as the Beatles were breaking through and as James Bond's virile British suavity became the biggest export in international cinema. After generations of stuffiness, empire, and warfare, the United Kingdom's capital city had become a hotbed of artistic fecundity, unrivaled in terms of breadth, depth, and influence to this day. Postwar gloom finally gave way to Carnaby Street Technicolor, and an entire nation seemed to loosen. But the prizes—notably sex, drugs, and rock 'n' roll—also became pitfalls.

Lambert & Stamp was painstakingly assembled over many years by director James D. Cooper, whose bulldog filmmaking style suits his subjects. 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 men behind the band. 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. Despite the predictable narrative, 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 all parties appear to be as amazed as we are at the remarkable, weird, tragic, triumphant story of their lives.

Lambert & Stamp comes at a bountiful time for Who devotees. 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 & 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 must come from the release date of their first single, "I Can't Explain"). Cooper's terrific documentary is an essential addition to the canon of one of the most-documented careers in music history, providing more insight than ever into an incredibly mismatched group of men that made violent, impassioned, often misunderstood music. recommended