On May 21, 1980, The Empire Strikes Back—the second film in the Star Wars series—arrived in theaters and thrilled audiences. Here are 10 fascinating facts about one of the most frequently misquoted films in the history of cinema.

1. The Empire Strikes Back's "big reveal" may not have been such a big secret after all.

Mark Hamill and David Prowse in The Empire Strikes Back (1980).© Lucasfilm Ltd. & TM. All Rights Reserved.

Much has been made of the lengths to which George Lucas and his fellow filmmakers went to keep the revelation that (spoiler alert?) Darth Vader is Luke Skywalker’s father under wraps. In a 2004 interview with Sound & Vision, Mark Hamill shared that “it was a wonderfully hard secret to keep because [Irvin] Kershner, the director, brought me aside and said ‘Now I know this, and George knows this, and now you're going to know this, but if you tell anybody, and that means Carrie or Harrison, or anybody, we're going to know who it is because we know who knows.'"

But the truth is that anyone who picked up the novelization of the movie, which was released a month prior to the film, would have known the plot twist already. (Good thing Twitter didn’t exist in 1980.)

2. David Browse spilled the beans on Luke Skywalker's connection to Darth Vader in 1978.

Two years before The Empire Strikes Back novelization hit bookstore shelves, a crowd of approximately 1000 Star Wars fans gathered in Berkeley, California to meet David Prowse, the man in Darth Vader’s suit. Believe it or not, Prowse shared that critical plot point with the crowd. A newspaper clipping from 1978 teased the genetic connection, even quoting Prowse as saying, “Father can’t kill son, son can’t kill father.”

3. The Empire Strikes Back's most memorable line is also its most misquoted.

When Darth Vader drops the paternal bomb on Luke, he does so by stating, “No, I am your father.” The line is one of the most often misquoted in cinema history, and usually repeated as “Luke, I am your father.” (Yes, even Chris Farley got it wrong in Tommy Boy.)

4. Monty Python and the Rolling Stones made Han Solo and Princess Leia smile.

In 1999, Carrie Fisher penned an essay for Newsweek on her Star Wars experience and recounted the time she and Ford pulled an all-nighter at a party with Eric Idle and the Rolling Stones. “Eric had just come home from filming Life of Brian in Tunisia,” Fisher wrote. “He brought this drink that he said they gave the extras so they'd work longer. I called it Tunisian Table Cleaner. As a rule I'm allergic to alcohol, and Harrison doesn't really drink either. But that night, there was a makeshift party. The Rolling Stones were there ... We stayed up all night and drank the table cleaner and never went to sleep."

When Fisher and Ford arrived to the set the next morning, "we weren't hungover," Fisher wrote. "We were, like the extras in Tunisia, more than willing to work. That morning we shot our arrival at Cloud City, where we meet Billy Dee Williams. And it’s one of the very few times in the series both Harrison and I smile. To this day, Eric is proud as a papa of his impact on the trilogy.”

5. George Lucas wanted Jim Henson to play Yoda.

In an interview with Leonard Maltin, Lucas admitted that he wanted Muppets maestro Jim Henson to play the role of Yoda. “I went to Jim [Henson] and said, ‘Do you want to do this?’ And he said, ‘Well, I’m busy, I’m doing this, and doing that, I’m making a movie and all that—I really can’t, but ... how about Frank [Oz]? You know, Frank’s the other half of me.’ And I said, ‘Well, that’d be fantastic.’”

Henson also recommended creature designer Stuart Freeborn, who explained that, “I was the one who kind of put all the elements of Yoda together, and although Jim didn’t make Yoda, George and he had an understanding that they would exchange technology information. George would give to Jim and Jim would give some of his people to George to help. Wendy Froud helped out a little bit with the character and two other people from Jim’s company worked the cables for me.”

6. Frank Oz says George Lucas didn't want him for the voice of Yoda.

In a 2014 interview, Oz, the normally reclusive puppeteer and director, said that, “George didn't want my voice in the beginning. I gave him a tape. He said, 'No thank you.' And in post-production for about a year I heard that he was auditioning voices for Yoda. He had no intention of using me for the voice. Then I was on my honeymoon with my first wife about 25 years ago or 30 years ago, and he [called and] said, ‘Frank can you come out … I think we'd like to try your voice.’ So I flew back and recorded Yoda.”

7. The Empire Strikes Back marked the end of Gary Kurtz and George Lucas's partnership.

Though it’s George Lucas’s name that’s most synonymous with the Star Wars universe, producer Gary Kurtz—who came up with the title for The Empire Strikes Back and also served as an uncredited assistant director—was an essential contributor to the first two films. Yet the pair ended their partnership following The Empire Strikes Back.

“I could see where things were headed,” Kurtz told the Los Angeles Times in 2010 of his reasons for stepping far, far away from Lucas’s film galaxy. “The toy business began to drive the [Lucasfilm] empire. It's a shame. They make three times as much on toys as they do on films. It's natural to make decisions that protect the toy business but that's not the best thing for making quality films.”

8. The Emperor used to be a chhimp.

In the original version of the film, the scene in which Darth Vader converses with the Emperor used to look a lot different. Though many viewers automatically associate the character with actor Ian McDiarmid, the original Emperor was an old woman with chimpanzee eyes and the voice of Clive Revill. (You can see both versions side-by-side above.)

9. Mark Hamill wasn't a fan of some of George Lucas's tinkering with The Empire Strikes Back.

While fans have long lamented the many changes Lucas has made to the original trilogy over the years, even Luke Skywalker himself wasn’t crazy about some of them. “I can't say I cared for that scream they added to the Special Edition (now gone), when Luke sacrifices himself [in The Empire Strikes Back],” Mark Hamill told Sound & Vision. “Kersh and I talked about the fact that when he actually reaches the point whether he has to join them or not, he lets go. It's like he's committing suicide rather than going to the Dark Side. So it is a calm thing. Look, it’s [George's] to tinker with as he sees fit. I always say it's his train set, if he wants to put up new billboards and new landscaping … Remember the old, ‘It's good to be the king?’ I guess George is ‘It's good to be The Emperor!’ If he wants to make them into musical comedies, that's his choice.”

10. Cliff Clavin has a small role in The Empire Strikes Back.

John Ratzenberger in The Empire Strikes Back (1980).© Lucasfilm Ltd. & TM. All Rights Reserved.

Two years before he began his decade-plus run as Boston mailman/trivia expert Cliff Clavin on Cheers, and a full 15 years before he began voicing Hamm in the Toy Story series, John Ratzenberger made an early-career appearance as Major Bren Derlin, part of the Rebel Force in The Empire Strikes Back. While he loved being part of such a major film franchise, what he remembers most is how “I somehow got a parking space next to Kermit the Frog. It was Jim Henson’s space, with this Kermit the Frog sign. So I took a photo of it and sent it to my mom with a caption that read, ‘Look, Mom. I made it. I got a parking space next to Kermit the Frog.’”