For truth in advertising, it’s hard to beat the title “Friedkin Uncut.”

This documentary about the great, not-forgotten but certainly under-heralded director of “The Exorcist,” “The French Connection,” “The Boys in the Band,” “Sorcerer,” “Bug” and “Killer Joe” is formless and right on the cusp of artless.

Its opening shot is of William Friedkin, who will turn 84 August 29, rolling up to his art-filled L.A. mansion in his Lexus.

For Pete’s sake.

He starts off rattling on about Hitler and Jesus, backpedaling to ensure nobody thinks he admires them both equally. “Good and evil,” he’s making a point about. Sort of.

And therein lies the triumph of the film. It is William Friedkin himself, a lovely old man of the cinema, a raconteur with a sort of Trumpian flare for hyperbole, rambling and not false, but somewhat inauthentic modesty. He’s a hoot.

So it doesn’t matter that this documentary appreciation spends silly amounts of time following Friedkin to French, Italian and Spanish film festivals, where he’s feted. It doesn’t matter that the documentary’s director is a little-credited actor (a “footman” in “The Grand Budapest Hotel”) turned first-time movie maker and comes off, at times, as wincingly out of his depth.

The film’s “star” and his work, his actors, his peers, his filmdom fans are all that matter. And they’re packed into this 107 minute biography and fan letter.

“Exorcist” star Ellen Burstyn breaks down why the film works, that “It starts on a very real level” and “step by step” moves to the horrific, which is why it scares the dickens out of people. Then she remembers how the great Max Von Sydow, whom Friedkin calls “the greatest actor in the world…at the time” kept blowing his line, “The power of Christ compels you!”

Maybe his atheism had something to do with that, they allow.

Friedkin relates the story of hiring Stacy Keach, and then letting himself get talked into replacing him with Pulitzer Prize-winning playwright and sometime actor Jason Miller.

And we’re off, with Francis Ford Coppola praising his directing contemporary telling stories “in the most direct possible way…He doesn’t philosophize about evil. He shows it.”

From action auteur Walter Hill (“48 Hours,” “Southern Comfort”) to horror master Dario Argento, Wes Anderson and Quentin Tarantino to Edgar Wright (“Hot Fuzz”), and Philip Kaufman (“The Right Stuff”), who went to high school in North Chicago with Friedkin, all are here to marvel over the movies and pay their respects.

The actors? Juno Temple and Matthew McConaughey (“Killer Joe”), Gina Gershon and Michael Shannon (“Bug”), Willem Dafoe and William Peterson (“To Live and Die in L.A.”) all talk about Friedkin’s “method,” treating actors like their characters, challenging them.

The fact that we don’t hear from Gene Hackman (“The French Connection” movies), Al Pacino (“Cruising”) or anybody from the many bombs that put his career in the shadows in the ’80s into the ’90s (“Deal of the Century,” “The Guardian,” “Blue Chips”) sticks out.

Maybe they were underwhelmed by the documentarian’s credits, too.

Technique? Friedkin likes to get what he wants in a single take. He’s always gone for “spontaneity” over “perfection,” he admits, pointing to “bad” shots that made it into his movies.

They shot the most famous chase in screen history, in “The French Connection,” on the fly in New York on a Sunday morning.

What’s that “spontaneity” do to actors?

“There’s no holding back, no charming your way through the scene,” Michael Shannon says.

“Rehearsal is for sissies. Rehearsal… is for dummies,” Friedkin declares.

“You just let it rip, from take one,” Matthew McConaughey offers.

Tarantino talks about how no filmmaker since can make the claim that the movie they’re making is too difficult, “challenging,” or “dangerous.” Not if it’s not as difficult as Coppola’s “Apocalypse Now,” as Werner Herzog’s “Aguirre, the Wrath of God” or as Friedkin’s jungle masterpiece, “Sorcerer.”

The best line from somebody not Friedkin in “Friedkin Uncut” comes from Coppola.

“Both ‘Sorcerer’ and ‘Apocalypse Now’ were made at a time when if you wanted to show something extraordinary you had to DO something extraordinary. And film it.”

Suck on that, Christopher Nolan.

And after Tarantino has talked up how one learns to stage and shoot a chase scene, on foot or in a car, by watching Friedkin, the master gets off a zinger.

“When it comes to chases, nobody can top Buster Keaton.”

The odd hilarious, profane declaration, leading a film festival audience as he sings “Singin’ in the Rain,” and too many shots of Friedkin getting coffee, “directing” his director and what not, the formlessness becomes a big part of the charm here.

A director who speaks of his “craft” and “professionalism” and pooh poohs “art,” a damned fine documentarian in his own right (Check out this interview/film he did with the great German master Fritz Lang on Youtube), you know William “Billy” Friedkin wouldn’t have it any other way.

MPAA Rating: unrated, screen violence, sexual situations, profanity

Cast: William Friedkin, Ellen Burstyn, Wes Anderson, Quentin Tarantino, Juno Temple, Dario Argento, Willem Dafoe, Gina Gershon, Francis Ford Coppola, Walter Hill, and Matthew McConaughey

Written and directed by Francesco Zippel. An AMB Distribution/QUOAIT release.

Running time: 1:47