Tumblr cinephiles have a new favorite movie this week. It’s decades old, so maybe you’ve already seen it. It is called “Goncharov” and stars Robert DeNiro in the titular role as a Russian hit man and former discothèque owner. It takes place in Naples, Italy. Cybill Shepherd plays his wife, Katya, and rounding out the cast are Al Pacino, Gene Hackman and Harvey Keitel.

The 1973 film, billed as “Martin Scorsese presents,” has everything: murder, a love triangle, homoerotic undertones, a striking original score and a dramatic final scene that film buffs have been debating for years.

There’s only one other thing to know about “Goncharov.” It does not exist.

The story of Tumblr’s beloved fake film began with a shoe. Several years ago, a Tumblr user posted a photo of a pair of “knockoff boots” they ordered online that arrived with a strange tag. “The greatest mafia movie ever made,” read the top line. “Martin Scorsese presents GONCHAROV.” “Domenico Proccacci production,” it continued. “A film by Matteo JWHJ0715.” “About the Naples Mafia,” read the final line. (The user’s Tumblr is no longer active and attempts to reach the user were unsuccessful.)

In August 2020, Aveline McEntire, a college student in Missouri, reblogged the image on her personal Tumblr after seeing it on a friend’s page.

Ms. McEntire added an additional image to her reblog, a screenshot of a comment from a third Tumblr user, reading, “this idiot hasn’t seen goncharov.” Ms. McEntire, 20, had not thought much about the post until recently when it suddenly started gaining popularity, with tens of thousands of people beginning to reblog it earlier in November.

As of Monday evening “Goncharov” was the No. 1 trending topic on the platform, with Mr. Scorsese taking the second spot. Pokémon was in third.

Even Tumblr has gotten in on the act. “Goncharov” was ahead of its time “and it’s contribution to cinema is remarkable,” the platform tweeted on Sunday from its official account. “Rarely does a film tell as many diverse-yet-interconnected stories. Hard to imagine so few ppl have seen it.”

On Tumblr, users have created an entire universe to support the idea that “Goncharov” is real. A poster for the film, riddled with bullet holes and crediting Matteo JWHJ0715 as the director of the “greatest mafia movie (n)ever made,” was created by Alex Korotchuk, a 20-year-old-artist in Prague, who said 50 people have placed orders to buy a print version of the poster. Alix Latta, a 25-year-old music teacher in Indiana, composed a theme song — a waltz inspired by the theme from “The Godfather.”

There are Tumblr posts full of lore about the film and vivid details about the plot, including stills and GIFs pulled from other films and TV shows being repurposed as scenes from “Goncharov.”

“It’s essentially a Russian gangster coming to Naples, and it’s a long story about his eventual downfall and betrayal by everyone in his life,” said Erika Paulson, 27. “To quote one of the posts that’s been going around, it’s him coming to Naples to try and escape his life of violence.”

A frequent Tumblr user, Mx. Paulson, who lives in Philadelphia, remembered seeing the “Goncharov” boots years ago and was excited to contribute to the story, posting several pictures of a cat, now known by some on Tumblr as Patchka, with the caption, “anyway i think we all know who the true best character in Goncharov (1973) is.” People have pointed out the cat could be another nod to “The Godfather,” but Mx. Paulson was inspired by street cats spotted on a trip to Rome. “What’s a gangster movie without a cat?”

Lynda Carter got in on it too on her Tumblr. The “Wonder Woman” star posted two black-and-white photos of herself and Henry Winkler captioned, “Me and ‘The Fonz’ at premiere of Goncharov (1973) at Grauman’s Chinese Theatre.” The image is actually a photo of the two actors at the 1977 Golden Globe Awards. A representative for the movie reviewing platform Letterboxd said it had removed multiple user reviews of the fake flick.

Elena Asofsky, 23, initially fell for the mythmaking. “I start asking my roommates. I’m like, ‘Hey, have you heard about this ‘Goncharov’ thing? What is this? Can we get in on it?’ And my roommate’s like, ‘I know, it’s fake. It’s all not real.’” Since then, Ms. Asofsky, a substitute teacher and illustrator in Columbus, Ohio, has been making fan art inspired by the imaginary movie.

Mx. Paulson pointed out Tumblr users have a rich history of this very particular brand of creativity, recalling how users several years ago created a similarly real fandom for “Squiddles,” a fictional TV show within the universe of the web comic “Homestuck.” But for some Tumblr users, it can be frustrating to be on the outside of inside jokes when other users refuse to cave and admit the thing they are talking about isn’t real.

That’s not what’s happening with “Goncharov” though, according to Dani Mays, an illustration student in Kansas City, Mo. “When that happens, it feels like they’re laughing at your expense, watching you get increasingly frustrated at the dissonance and taking that frustration as part of the bit, turning you into part of the punchline,” Ms. Mays, 24, wrote in a popular post on Tumblr. “I’m not seeing any of that with Goncharov, at least as far as the more popular users participating in it.”

“The fact that people are so willing to break the joke long enough to tell people what’s going on and then bring people into the fold, so to speak, is nice,” Ms. Mays added in a phone interview with The Times.

How the title “Goncharov” came to be on the boot’s tag in the first place continues to be a mystery. Michael Littrell, a musician from Minneapolis, has a theory. After seeing the boots floating around Tumblr for years, Mr. Littrell, who studied journalism in college, started investigating in October and eventually came across an Italian producer named Domenico Procacci. (The same producer named by the boots.) From there, he connected the dots to a 2008 film called “Gomorrah,” about Italian organized crime.

Mr. Scorsese was not the director, but according to Mr. Littrell, 24, and a years-old story from The Hollywood Reporter, “Gomorrah” had a presentation credit from the famed director when it arrived in the United States.

A poster Mr. Littrell found in his search reads “Martin Scorsese Presents” at the top and is stylized much the same as the boots’ label, with Mr. Scorsese’s name in red and the title of the film in capitalized black letters. The director of “Gomorrah” is Matteo Garrone. Who shares a first name with Matteo JWHJ0715.

A tagline proclaims “Gomorrah” to be “BASED ON THE BEST SELLING EXPOSÉ BY ROBERTO SAVIANO ABOUT THE NAPLES MAFIA.” Details that bear a striking similarity to the boots that started this whole saga.

“I really want Scorsese to see this and maybe make Goncharov,” reads a reply on Mr. Littrell’s Tumblr post documenting his findings.