35 years ago today, Ivan Reitman’s iconic fantasy comedy Ghostbusters, made its debut in theatres. Released on June 5, 1984, Ghostbusters, starring Bill Murray, Dan Aykroyd, Sigourney Weaver, Harold Ramis, and Rick Moranis, became an instant success, grossing over $295 million worldwide, making it the highest-grossing comedy of its time.

Since then, the Ghostbusters franchise has gone on to produce a sequel in 1989, an awesome TV series, various comic books and video games, and a less than popular all-female reboot film in 2016. A new Ghostbusters film, directed by Jason Reitman, is currently in development and scheduled to release in the July 2020.

In celebration of Ghostbusters’ 35th anniversary, here are 10 things you probably didn’t know about the original Ghostbusters film.

10. Michael Keaton Was Originally Cast as Peter Venkman

Dan Aykroyd was writing the script for Ghostbusters in 1982 when his best buddy John Belushi died of a drug overdose. While Aykroyd had Belushi in mind to play lead scientist Peter Venkman, his pal died before the script was finished and casting the film had begun. By the time the movie was ready to go into production, director Ivan Reitman and Dan Aykroyd had settled on actor Michael Keaton to play Peter Venkman. They felt that Keaton’s fast-talking and sarcastic screen persona would be perfect for the role. Michael Keaton read for the part and was cast. However, when Dan Aykroyd’s other good friend and Saturday Night Live castmate Bill Murray expressed interest in the part, it was decided to retool and cast Bill Murray instead. It didn’t hurt that director Ivan Reitman had previously directed Bill Murray in the films Stripes and Meatballs.

9. Slimer’s Real Name is “Onion Head.”

The most popular and iconic ghost in the first movie is the fat green one that appears in the hotel hallway and “slimes” Bill Murray’s character Peter Venkman at the start of the movie. This ghost character, who only appears in the one scene in the film, has become known collectively by audiences as “Slimer,” and has become a de facto mascot for the Ghostbusters. However, the character is never given a name in the movie. It was audiences and the media that dubbed the ghost “Slimer” due to the fact that it slimes Murray in the movie. On the set, the cast and crew referred to the ghost as “Onion Head” because it was seen eating from a room service cart and was supposed to have really bad breath. Also on the set, actor/writer Dan Aykroyd jokingly referred to Slimer as the “ghost of John Belushi,” whose death was still raw for the cast at the time of filming in 1983.

8. Huey Lewis Sued Ray Parker Jr. Over Ghostbuster’s Theme Song

Ray Parker Jr. had a massive hit song (his only one) in 1984 with the theme song to Ghostbusters. The catchy line “I ain’t afraid of no ghost” could be heard everywhere in the summer and autumn of 1984. However, the song was not beloved by everyone. Fellow musician and hitmaker Huey Lewis sued Ray Parker Jr. over the Ghostbusters theme, claiming that it was too similar to his hit song “I Want A New Drug” that had come out the year before. The lawsuit was acrimonious and dragged on for 11 years until a settlement was finally reached in 1995. Details of the settlement were not released publicly, but Ray Parker Jr. turned around and sued Huey Lewis in 2001 after Lewis publicly mentioned the lawsuit. Ray Parker Jr. claimed that Huey Lewis was contractually obligated not to discuss the lawsuit in public.

7. A Real 1-800 Number Was Created To Promote The Movie

The phrase “Who ya gonna call?” is central in the film, and is even mentioned in the theme song. To capitalize on the phrase and help promote the movie ahead of its release, producers of the movie established a real 1-800 number for people to telephone in the summer of 1984. The phone line featured a pre-recorded message by Ghostbusters stars Bill Murray and Dan Aykroyd. While producers initially viewed this as a promotional stunt, the 1-800 phone line became very popular and actually received more than 1,000 calls an hour for six weeks during the movie’s run in theaters. Eventually, the 1-800 number was canceled, and a non-functioning “555” number is featured in the film.

6. The Phrase “I’ve been slimed” is Never Said in the Movie

The most popular catchphrase from Ghostbusters is never actually said in the film. In 1984, t-shirts and baseball hats everywhere read “I’ve been slimed,” in reference to Ghostbusters. In particular, it referenced the scene in the movie where Bill Murray gets slimed in the hotel hallway by the ghost known as “Slimer.” However, in the movie, Bill Murray actually says “He slimed me.” Nowhere in the movie does any character actually utter the popular phrase “I’ve been slimed.” Yet it was that catchphrase that appeared everywhere after the movie was released and became a bonafide box office hit in the summer of 1984.

5. The Proton Packs Evolved Over Two Films

The Proton Packs that the Ghostbusters carry on their backs and use to zap ghosts into submission were never well thought-out ahead of filming and evolved over the course of the first two movies. In fact, the term “Proton Pack” is not actually used until halfway through the sequel, Ghostbusters II. The Proton Packs were originally just wands that the Ghostbusters used similar to the “sick sticks” featured in the movie Minority Report. The props department added the backpacks during filming. And the idea that crossing the streams of the Proton Packs would lead to an explosion was made up on the spot while the main actors were ad-libbing the final scene of the movie. This is amusing considering how associated the Proton Packs are with the Ghostbusters franchise.

4. Director Ivan Reitman is the Voice of Zuul

The deep and menacing voice of evil ghost/spirit Zuul is one of the most memorable things from Ghostbusters. And if you’ve ever wondered who performs the voice of Zuul in the movie, it is none other than director Ivan Reitman. During post-production on the film, Ivan Reitman was looking around for an actor to voice Zuul but was having trouble finding one. Out of time and with a release date for the movie fast approaching, Ivan Reitman decided to perform the voice himself. Using his best baritone, Ivan Reitman performs the voice of Zuul and did it so well that the cast and crew were blown away when they saw the final version of the movie. Many people involved in the Ghostbusters production didn’t realize it was Ivan Reitman performing the voice.

3. Eddie Murphy Was Originally Cast to Play Winston Zeddmore

Eddie Murphy was red hot in 1983 when Ghostbusters began filming, and he was actually cast to play the role of the black Ghostbuster, Winston Zeddmore, who joins the team halfway through the movie. Murphy, who has made his own attempts at sci-fi comedy films (see The Adventures of Pluto Nash), loved the script and was keen to work with fellow SNL alumni Bill Murray and Dan Aykroyd. Sadly, Eddie Murphy was contractually bound to star in another little film that came out in 1984 called Beverly Hills Cop. And when a scheduling conflict arose, Eddie Murphy had to bow out of the movie and was replaced by actor Ernie Hudson. This missed opportunity is made sadder by the fact that the criticism leveled at the character Winston Zeddmore is that he has no real personality in the film and, as played by Ernie Hudson, is not funny. Alas, fans are left to wonder what might have been had Eddie Murphy been able to take the role.

2. Bill Murray Made No Money From The Movie

Made on a budget of $30 million, Ghostbusters went onto gross nearly $300 million in 1984 – a then-astronomical sum. In fact, Ghostbusters was the highest grossing comedy in movie history until Home Alone supplanted it in 1990. Yet despite the movie’s success, star Bill Murray didn’t make any money off, arguably, his most financially successful movie. This is because rather than take a paycheck for Ghostbusters, Bill Murray negotiated with Columbia Pictures to finance his personal pet project, a remake of the movie The Razor’s Edge, about a World War I veteran who goes searching for the meaning of life after being scarred by war. Bill Murray co-wrote the script for his film version of The Razor’s Edge and it was his first dramatic role. Released in October 1984, The Razor’s Edge was a critical and commercial bomb. Made for a budget of $12 million, it grossed only $6 million in theaters. Audiences and critics were not ready for a serious Bill Murray, especially after he cracked everyone up earlier that year in Ghostbusters.

1. The Movie Was Originally Called “Ghost Smashers” and Was Set in the Future

Dan Aykroyd started writing the screenplay for what would become Ghostbusters in 1981 and spent nearly two full years on it. The movie’s original title was Ghost Smashers and the screenplay was nearly 500 pages long. The original story was set in the future where there were many different teams of Ghostbusters competing against one another. Ivan Reitman found the screenplay way too long and convoluted, and he hated the title. Actor and writer Harold Ramis was then brought in to help Dan Aykroyd focus on the script. It was Harold Ramis’ idea to turn the movie into what he called “a going into business film.” After much reworking, the script became much leaner and the title changed to Ghostbusters, and the rest, as they say, is history.