Film fan lore has long implied that Steven Spielberg, the producer of the horror blockbuster “Poltergeist,” was really its director or at least co-director.

The 1982 film has Spielbergian touches — compositions, classical editing, the striking lighting and the inclusion of and affecting performances by children. He was on a roll at the time and could seemingly do no wrong and was given much of the credit for the film’s success.

But all of that had the effect of diminishing the artist actually behind the camera, the long underrated horror icon Tobe Hooper. He made many more movies, but his reputation suffered and his career never had the kind of trajectory a smash hit/cultural touchstone thriller should have served up.

The college professor, whose worldview and art were informed by witnessing the infamous mass shooting by sniper Charles Whitman at the University of Texas in 1966, widely regarded as one of the most influential horror filmmakers ever, more than gets his due in the new documentary “Chain Reactions.”

The title may be a glib pun on the movie Hooper made infamous, “The Texas Chain Saw Massacre.” And its first interview is with a standup comic, Patton Oswalt, who long did a bit arguing that “A movie title should let you see a mini movie in your head,” tell you everything you need to know in four or five words.

“Best. Title. EVER? ‘Texas CHAIN SAW Massacre!”

But this film, from the director of “Leap of Faith: William Friedkin on ‘The Exorcist,'” is a deep, incisive, celebratory and cerebral dive into the “art” of Hooper’s most imitated work.

Stephen King, who worked with Hooper on a couple of projects, practically sings his praise about the movie’s notorious cheapness, its “washed-out ’70s” visuals, with even the grainier and grainier prints (it was shot on 16mm and blown up to 35mm initially) and worn VHS tape viewings patina adding to its impact.

“It looks f—–g REAL!”

Karyn Kusama, director of “Girlfight,” “The Invitation” and episodes of “Halt and Catch Fire” and “Yellowjackets,” unwinds the politics, cultural warnings and “the saddest, scariest depiction of (broken) masculinity ever seen on film.”

With his film of dim-witted, violent and obsolete blue collar (and rural) Americans preying and eating young people (“hippies”) who fall into their clutches, “the young artist (Hooper) was looking into the future of America.”

Japanese horror icon Takashi Miike (“Ichi the Killer,” “One Missed Call”) marvels at how his fate was sealed the day he missed a showing of Chaplin’s classic “City Lights” and dropped in on a cinema showing “Chain Saw Massacre” instead, a movie that caused a revolution in Japanese horror cinema, setting the table for “J-horror.”

Miike and King embrace the “lack of morality” of Hooper’s creation, the extremes it goes to. Kusama talks about how unpleasant it is to sit through and how much more unpleasant it can be to watch again.

All mention how “the story makes no sense,” the “acting” is so “amateur” as to make the viewer believe serial killers “have gotten their hands on a film camera” and are documenting their work.

And Australian critic Alexandra Heller-Nicholas notes “Chain Saw Massacre’s” influence on generations of Australian cinema, largely thanks to the fact that it was banned for years. Handing down VHS copies of a movie with “beautiful” flashes of nature and vivid colors in aging, yellowing hues made Australian movies imitating its “Outback yellow” look.

Scores of movies (“Nosferatu,” etc.) that predated “Chain Saw” or were influenced by it (“The Evil Dead,” “Midsommar,” “The Blair Witch Project,” of course) and are name-dropped and sampled. Great art works by Bacon and Bosch that Hooper either mimicked or “accidentally” paid visual homage to are compared to scenes and shots and sequences.

But Patton Oswalt is here to balance the critical parsing as the ultimate fanboy, geeking out over sequences, characters, messages and obscure other titles that connect to this brutal, unblinking and so-ugly-it’s-a-thing-of-beauty classic.

It’s not enough to make one want to go back to “Chain Saw.” Kusama got that right. But if you want an Ur Text for modern movie horror, from “Tales from the Crypt” to “torture porn,” there it is. And if you want to understand the genre, it remains the most essential viewing of any modern horror tale.

Rating: unrated, graphic, gory violence and nudity

Cast: Stephen King, Karyn Kusama, Takashi Miike, Patton Oswalt and Alexandra Heller-Nicholas

Credits: Scripted and directed by Alexandre O. Philippe. A Dark Sky release.

Running time: 1:44