Lorne Michaels, the inscrutable guru who changed Saturday nights in America by creating “Saturday Night Live” and then presiding over it for almost all of its 51 years, is the “star” and central figure of mystery of “Lorne.”

The documentary by Morgan Neville, the Alex Gibney of American pop culture documentarians, probably promises more than it delivers in getting at “the REAL Lorne Michaels,” and not the legend. Or the many “Doctor Evil” impersonations. Michaels still guards his family today and his upbringing way back when like treasured industrial secrets.

And scads of people he’s “discovered,” employed and “made famous” confirm as much in this still delightful dollop of Boomer — and Gen X etc. — “SNL” nostalgia.

Cast members from Tina Fey to Chris Rock on down to John Mulaney and Sarah Sherman, fellow Canadians Mike Myers and Martin Short and “close friends” Paul Simon and Steve Martin relay the “routines” that dominate the life and work of Michaels, who turns 82 in November.

We glimpse his lakeside Maine “blueberry farm” retreat, where he and his unseen third wife and family spend most of the weeks and months that “SNL” is on hiatus. And his ex-wife and onetime “SNL” writer Rosie Shuster talks about him and the show, but nothing comes out that Michaels wouldn’t approve.

Still photos, home movies and animated snippets barely touch on the childhood, the father who died when Lorne Michael Lipowitz (one of the legions of Lorne impersonators groans on Michaels’ behalf at this mention) was young, so there’s little hint of the formative years before he got on Canadian TV, then went to LA and kick-started his career in “Laugh-In,” following that by working with Lily Tomlin on her post-“Laugh-In” specials.

But Neville and his crew sit in on the weekly Tuesday “host meets the cast” dinners at Manhattan’s Lattanzi Cucina Italiana on a week when Timothée Chalamet hosts “Saturday Night Live.” And the film crew is there during the weekly writer, performer and producers meeting where story pitches are made.

This is where cast members and writers, from Bill Hader and Paula Pell on back into the Tina Fey pasts revel in the memory of that time they “made Lorne laugh” and got his approval.

And Neville and we get to glimpse the process of winnowing 80 sketch ideas down to the 8-12 that Michaels announces to one and all make the final cut, sending writers and performers back to polish the scripts and get them ready for that hard, unforgiving deadline that drives this entire process, “11:30 Saturday night.”

Nostalgic Boomers who have watched the show from the start and anybody who has binged decades of “SNL” online can pick up on some between the lines “answers” to questions like “Why WAS Paul Simon on SO MANY episodes during the early years?”

He was Lorne’s neighbor.

The trauma of Michaels and the entire cast leaving after the fifth season is remembered, as is an abortive non “live” version of the series that NBC talked Michaels into attempting, “The New Show.”

Viewers and cast members can be tickled by clips of Michaels’ early TV efforts in Canada, where he “was a terrible performer” Michael Che notes, and often broke-up in sketches. Chris Rock adds, “The best coaches were lousy players.

Michaels often broke up in sketches. “Corpseing” they call it in the UK. Jimmy Fallon, perhaps the show’s most constant corpser (watch “More Cowbell”), shakes his head and jokes about the “therapy” he could have saved himself if he’d known the thing Michaels berated him for constantly was something the Executive Producer never conquered.

Not “everybody” is here. Nor is every highlight and low point. How could they be? Fifty years, thousands of sketches that became classics, or epic misfires, scores of cast members, famous and infamous, there wasn’t time or room for everyone. And so few claim to actually “know” this film’s subject more voices might not have helped.

Michaels jokes that one reason the show has endured and even its earliest seasons dominate Youtube is that it “clips well,” as legendary bits only have to be briefly sampled on video for the viewer to guffaw over what made “Julia Child” or “Cowbell” or Ryan Gosling’s corpsed collapse in a “Beavis and Butthead” bit endure.

Michaels himself is reasonably forthcoming about process. “Fatigue is your friend” on those Thursday night marathon writing sessions where “edge” and “hard laughs” come when the writers are punchy and uninhibited. But Michaels maintains his “mystery” even bantering with frequent host Steve Martin and others who really “know” him.

Mulaney, Rock and Che have the best anecdotes. Fey may be the one who really “gets” him, as she shows us how she based Alec Baldwin’s character on her Lorne-produced sitcom “30 Rock” on Michaels.

One and all note how “he made so many of us (rich and) famous.”

But the most telling read on “the boss” and why, in his ’80s, he still has “the eye” and ear and savvy to pick up on “what the kids are laughing at these days,” might come from current cast member Sarah Sherman.

“He takes, like, 24 year olds really seriously.”

Every generation of players, many of them getting their start in their early ’20s, is heard and valued, even when the boss has a vast collection of put-downs about how soon they’ll be fired, the show will be canceled or the network will go bankrupt because this or that sketch, line or performance isn’t landing.

That has to be the key to Michaels’ success and longevity in a profession where “old guys can’t do comedy” is the law. And taking “24 year-olds really seriously” has made Michaels “the guy who stays…the ultimate show business survivor.”

Rating: R, profanity

Cast: Lorne Michaels, Tina Fey, Chris Rock, Steve Martin, Mike Myers, Paul Simon, Michael Che, Colin Jost, Paula Pell, Maya Rudolph, Dana Carvey, John Mulaney, Candace Bergen, Martin Short, Howard Shore, Adam Sandler and Steve Higgins.

Credits: Directed by Morgan Neville. A Focus Features release now streaming on Netflix, Amazon, etc.

Running time: 1:41