Once ‘Sidemen,' they finished as the stars

All rock 'n' roll roads lead back to the blues. And if “Sidemen: Long Road to Glory” is to be believed, most of those highways converge on three Delta bluesmen in particular: the drummer Willie Smith, the guitarist Hubert Sumlin and the pianist Joe Willie Perkins, known as Pinetop.

Germinating and shape-shifting for almost a decade, Scott Rosenbaum's loving tribute (originally conceived in 2008 as a “Last Waltz”-style concert film) pulls back the big-name curtain to celebrate these often overlooked backing musicians whose riffs and runs are revered to this day. Thanks to such British disciples of American blues as the Rolling Stones and Eric Clapton, who would subsequently pass the torch to Jimi Hendrix and the Allman Brothers, and, later, the White Stripes and the Black Keys, the trio of surviving Muddy Waters and Howlin' Wolf sidemen suddenly found themselves in demand.

As proof, a slew of sunken-eyed rock legends - including Johnny Winter, Gregg Allman, Keith Richards and Joe Perry - is on hand to share memories of the men and attest to their lasting influence.

But “Sidemen” is about more than just legacy. Blessed with extensive interviews with their buoyant subjects (all three of whom died in 2011 within months of one another), Rosenbaum and his producer Jasin Cadic shape a narrative of professional insecurity and personal resilience.

From playing brothels and juke joints in the Jim Crow South to decades-long collaborations with the Chicago blues pioneers Muddy Waters and Howlin' Wolf, the three weathered careers of astonishing flux.

Their stories are inseparable from that of the blues itself, which the filmmakers illustrate with a wealth of clips and concert footage reaching back more than half a century. The kids who thrilled to the Rolling Stones performing “Little Red Rooster” (the first blues song to reach No. 1 on the British charts), or watched Jimi Hendrix kill “Killing Floor,” probably knew nothing of Wolf and Waters. They just knew what they liked.