Those who were offended by The Producers (and there were many) didn’t shy away from saying so. A few months after the film’s release, writer/director Mel Brooks was on an elevator in New York City when a woman noticed him and said, “I have to tell you, Mr. Brooks, that your movie is vulgar.” “Lady,” he replied, “it rose below vulgarity.” Indeed it did. Utterly fearless, this classic comedy joked about every taboo subject the late 1960s had to offer—including LSD, transvestitism, and of course, Adolf Hitler.

1. IT WAS INSPIRED BY SOME ACTUAL BROADWAY PRODUCERS.

The truth is just as strange as fiction. When Mel Brooks was 16 years old, he worked for a cash-strapped theatrical producer who’d raise funds by sleeping with his investors—most of whom were elderly women. “He pounced on little old ladies and would make love to them,” Brooks told The Guardian. “They gave him money for his plays, and they were so grateful for his attention.” In Manhattan, Brooks also knew a pair of showmen who had more or less failed their way into prosperity. “[They] were doing flop after flop and living like kings,” Brooks said. “A press agent told me, ‘God forbid they should ever get a hit, because they’d never be able to pay off the backers!’ I coupled the producer with these two crooks and—BANG!—there was my story.”

2. ONE STUDIO WANTED TO REPLACE HITLER WITH MUSSOLINI.

Brooks originally titled the screenplay Springtime for Hitler, after the fictitious musical that drives the plot. Given the premise, it’s hardly surprising that a horde of studios passed on the script. Universal expressed some interest, but there was a catch: While meeting with Brooks, legendary studio head Lew Wasserman told him, “Instead of Hitler, make it Mussolini. Springtime for Mussolini. Mussolini’s nicer.” “Lew, I’m afraid you just don’t get it,” Brooks replied. In the end, the project was picked up by Joseph E. Levine of Embassy Pictures. “You want Hitler, you got Hitler,” he told Brooks. “Just don’t call it Springtime for Hitler.” So the film was rechristened The Producers.

3. ZERO MOSTEL’S WIFE CONVINCED HIM TO JOIN THE CAST.

The character of Max Bialystock was written with Zero Mostel in mind. Theatergoers adored the bombastic Mostel, who’d won Tony Awards for his leading roles in A Funny Thing Happened on the Way to the Forum and Fiddler on the Roof. At first, he wanted nothing to do with The Producers. Intent on casting him, Brooks asked Mostel’s wife, Kate, if she’d read the script. She did—and told Brooks, “It’s marvelous, it’s sensational. I’m gonna work on Zero until he does it.”

A week later, Brooks finally got the phone call he’d been waiting for. “You son of a bitch, I’m gonna do it,” Mostel told Brooks. “My wife talked me into it.”

4. MOSTEL EASED GENE WILDER’S NERVOUSNESS WITH A GIANT KISS.

Bialystock’s partner in crime is Leo Bloom, an accountant with some major self-esteem issues. Brooks wanted Wilder—whom he’d once described as a “perfect victim”—for the part. However, he didn’t dare hire him without first getting Mostel’s approval. And before that could happen, the two actors had to meet in person.

Back then, Wilder was still a relative unknown, so the thought of reading lines with a Broadway superstar made him extremely nervous. On the day of reckoning, Wilder arrived at producer Sidney Glazier’s office to find Brooks and Mostel waiting for him. And then Zero stood up. “This huge, round fantasy of a man came waltzing towards me,” Wilder wrote in his 2005 autobiography. “My heart was pounding so loud I thought he’d hear it. I stuck out my hand, politely, to shake his, but instead … Zero pulled me into his body and gave me a giant kiss on the lips. All nervousness floated away.”

5. THERE’S A FRANZ KAFKA REFERENCE.

It comes when we find Max and Leo busily looking for the worst play ever written. As they comb through a mountain of scripts, Max picks one up and reads the first sentence aloud. “Gregor Samsa awoke one morning to discover that he had been transformed into a giant cockroach,” he recites. After a split-second pause, he adds “It’s too good.” It actually is—that’s more or less the opening line of Franz Kafka’s The Metamorphosis. The original quote was “As Gregor Samsa awoke one morning from uneasy dreams, he found himself transformed in his bed into a gigantic insect.” Close enough.

6. KENNETH MARS SLEPT IN HIS COSTUME.

To help the other actors feel genuinely uncomfortable around his character, Kenneth Mars—who played Franz Liebkind, Springtime for Hitler’s bumbling, former Nazi playwright—he’d take his costume home and sleep in it every night—without laundering a single garment. “I did not smell like a rose,” Mars admitted.

7. WILDER’S DOG HELPED ENHANCE HIS PERFORMANCE.

Early in the movie, Max snatches Leo’s trusty blue blanket—and the accountant proceeds to throw a red-faced temper tantrum. In a 2002 “making of” DVD documentary, Wilder shed some new light on his frame of mind during this famous scene. “At the time, I had a little dog and I felt close to her,” he says. Hoping to give a more genuine performance, Wilder pretended that—instead of the blanket—Mostel had just snatched his beloved pooch. “I started to get a little crazy,” he admits. “I was getting upset because [in my head] Zero was grabbing that little dog and who knew what he was going to do to it?”

8. IT’S BEEN CREDITED WITH COINING THE TERM “CREATIVE ACCOUNTING.”

If you’ve ever taken a business ethics class, you know all about this concept. Essentially, creative accounting is the (legal) practice of interpreting financial laws in an atypical way. Oftentimes, this entails taking advantage of loopholes. Film critic David Ehrenstein argued that the phrase itself was born from an oft-quoted line in The Producers: Before Leo explains his grand scheme to Max, he says “It’s simply a matter of creative accounting.”

9. YOU CAN HEAR BROOKS’S VOICE IN THE “SPRINGTIME FOR HITLER” NUMBER.

Brooks has appeared in many of his movies, but he stayed out of The Producers—at least physically. Fast forward to 1:20 in the clip above and you’ll hear a member of the Springtime ensemble shout, “Don’t be stupid, be a smarty! Come and join the Nazi party!” Brooks didn’t like how the actor delivered that line, so he dubbed over it himself. (Hence the slight New York accent.)

10. PETER SELLERS HELPED PROMOTE IT.

Before Wilder was cast, Brooks offered Peter Sellers the role of Leo Bloom. For reasons unknown, he didn’t take the job (some say that he was too busy shopping at Bloomingdale’s to really listen to the pitch), but he was clearly a fan of the film. While filming I Love You, Alice B. Toklas! in Los Angeles, Sellers gathered some friends and set up a weekly film club. One week, when their plans to watch Federico Fellini’s I Vitelloni fell through, they put on The Producers.

Sellers loved every frame of it. Once the picture ended, he called Levine to congratulate him—at 2 a.m. Much to the actor’s dismay, he was informed that The Producers was in dire straits. After a disastrous test screening in Philadelphia, Embassy Pictures planned on shelving it. Luckily, Sellers convinced the studio to give it a broad release. Then he helped promote the movie further via full-page ads that he personally took out in Variety and The New York Times.

11. IT BEAT OUT SOME ELITE COMPETITION AT THE OSCARS.

Thanks in no small part to Sellers’s endorsement, The Producers became a respectable hit. Strong word of mouth about the film spread like wildfire and, in 1969, it was nominated for two Oscars: Best Supporting Actor for Wilder, and Best Original Screenplay for Brooks. Brooks’ competition in the latter category was fierce, and included Stanley Kubrick’s 2001: A Space Odyssey, one of the greatest science fiction movies of all time. Yet, groundbreaking as Kubrick’s picture was, The Producers took home the gold.

12. BROOKS PERSONALLY REPLIED TO EVERY JEWISH LEADER WHO CONTACTED HIM WITH A COMPLAINT ABOUT THE FILM.

Brooks has said that one of his “lifelong jobs” is “to make the world laugh at Adolf Hitler.” For Brooks, The Producers was a way to enact vengeance through comedy. “The only real way I could get even with Hitler and company was to bring them down with laughter,” Brooks said. But some viewers felt that the film actually promoted Hitler.

When The New York Times critic Renata Adler saw The Producers during its original run, she accused the movie of setting up an awful precedent. “I suppose we will have cancer, Hiroshima, and malformity musicals next,” Adler wrote in her review.

Furthermore, as the director himself recalled, “Jewish organizations at the beginning were outraged. They didn’t get the joke.” Within months of the movie’s release, Brooks received angry letters from, in his estimation, “every Rabbi in New York.” To the man’s credit, he took these very seriously. “I wrote [a reply to] every single letter I got, explaining ‘You can’t get on a soap box with Hitler. You’ve got to ridicule him.’”