In a recent segment of HuffPost Live, James Poulos spotlights one of my under-the-radar musical heroes: guitarist Waddy Wachtel.

I first encountered Wachtel through his work in Keith Richards’s solo band, the X-Pensive Winos. (In his memoir Life, Keith calls Wachtel a “guitar player extraordinaire, interpreter of my musical gropings … one of the most tasteful, simpatico players I know.”) From there, I came to realize his musical c.v. was like a game of “Six Degrees of Waddy Wachtel”: if he hadn’t played on a track personally, then for sure he’d played with someone who has played with someone who has…

Wachtel turned up in Poulos’s studio thanks to a new documentary film, King of the Sidemen, directed by Gary Simson. Originally conceived to document the live performances of an all-star pick-up band that Wachtel regularly leads in L.A., the project became, instead, a celebration of a wonderful synergy: a once-a-century web of musical creativity that connected Warren Zevon, Jackson Browne, James Taylor, the Eagles and their assorted SoCal associates, Stevie Nicks, Linda Rondstadt, and many, many others.

The unheralded presence of musicians like Wachtel on these recordings is a story that’s near and dear to my heart. With the great pianist Chuck Leavell as my subject, I wrote in the Washington Times, in 2005:

Some of rock’s most indelible moments are the work of sidemen, most of whom stay in the shadows, some of whom go on to achieve fame of their own. … Jazz guitar pioneer Charlie Christian was a prodigy within the Benny Goodman stable. Funk bassist Bootsy Collins was stuck behind James Brown, a notorious credit-hogger, before George Clinton gave him a more prominent role in Parliament.

A key test of an indelible sideman contribution is this: You shouldn’t be able to imagine a song without it.

Think of Al Kooper’s Hammond B-3 organ on Bob Dylan’s “Like a Rolling Stone.” Listen to an early, waltz-like version of the song on Mr. Dylan’s “Bootleg Series” boxed set; it sounds emasculated without Mr. Kooper’s touch.

Think of every Chuck Berry song on which pianist Johnnie Johnson played.

What would Neil Young’s “Southern Man” be without Nils Lofgren’s chugging piano chords? The Beatles’ “Get Back” without Mr. Preston’s electric piano solo? John Lennon’s “Jealous Guy” and the Who’s “Getting in Tune” without [Nicky] Hopkins’ gentle tunefulness? The Stones’ “Brown Sugar” without Bobby Keys’ wonderfully sloppy saxophone solo? Or Stevie Nicks’ “Edge of Seventeen” without Waddy Wachtel’s propulsive staccato guitar riff?

That a documentarian has succeeded in making a film about this topic, a film that, to date, has fetched more than $35,000 via Kickstarter.com—well, let me just say it makes me very, very happy: