The song "All Star" by Smash Mouth, heard in the opening credits, was only placed in the film for test audiences until a new song could be found. But test audiences loved it, and the producers kept it in. When the producers decided to keep "All Star" they decided to let the band sing the last song in the movie, "I'm a Believer."
The line "You're on your way to a smacked bottom." was improvised by Mike Myers after he got annoyed at one of the directors. He had also used this line a few years earlier, while playing his Austin Powers character in the popular music video of Madonna's song 'Beautiful Stranger'.
Chris Farley was originally cast as Shrek and even recorded almost all of the dialogue. However, after his death, the role was given to fellow Saturday Night Live (1975) performer, Mike Myers. Shrek's "air quotes" in the film is an homage to Farley, whose character Bennett Brauer also used air quotes. A story reel featuring a sample of Farley's recorded dialogue was leaked to the public in August 2015.
Mike Myers originally voiced Shrek with his natural speaking voice before the film was test-screened. Then he tried country Canadian accents for Shrek. However, after viewing a rough cut of the film, he felt that something was missing from his performance, and re-recorded all of his lines with a Scottish accent, based on the voice his mother used when reading him bedtime stories as a child. The original voice can still be heard in the technical goofs on the DVD. The decision to revoice Shrek in a Scottish accent ended up costing an additional four million dollars as it took him twenty sessions to complete the re-voiceover. It can also be stated that Shrek's accent is similar to the one Mike Myers uses for his character Fat Bastard in the Austin Powers series. This was his first voice performance in an animated film.
The scene where Princess Fiona burps was written after a recording session where Cameron Diaz burped after drinking Coca-Cola. Eddie Murphy improvised Donkey's response to Shrek, "She's as nasty as you are!"
The principal actors never met each other. They all read their parts separately, with a reader feeding them the lines. John Lithgow later admitted that, while he enjoyed playing Lord Farquaad, he was a little disappointed that he never actually worked directly with Mike Myers, Cameron Diaz, or Eddie Murphy.
Mike Myers was in New York City when they realized that the line "What are you doing in my swamp?!" had never been read. So producer Jeffrey Katzenberg flew to New York City, and had Myers read the line in the back of a limo.
When the fairytale creatures arrive at Shrek's swamp, you can see Papa Bear comforting Baby Bear at a fire... later in Lord Farquaad's castle, as he watches Fiona on the mirror you see Mama Bear as a rug, skinned and laying on the floor. Her ultimate fate, however, seems to be OK: she re-appears in the Video/DVD Karaoke scene, dancing with Papa and Baby Bears.
Cameron Diaz, having undergone Kung Fu training during the making of Charlie's Angels (2000), became very physical when recording her kung fu moves for Fiona's fight with Robin Hood and his Merry Men, and at times even broke out into Cantonese.
Steven Spielberg was originally going to produce the film in 1991, when he was in charge of Amblin Entertainment. Then, the film would have been in hand-drawn animation, and was going to star Bill Murray as Shrek and Steve Martin as Donkey.
The song "Welcome to Duloc", which is sung by the wooden dolls in the cabinet at the entrance to Duloc, is not only a parody of Disney's "It's a Small World", but is in the same key and has the same beats per minute (tempo) as the Disney song.
Prior to release, the movie was viewed by DreamWork's lawyers, since there were concerns that Disney would sue over the movie's not-so-subtle satirical references to the company's films and theme parks.
A fairy godmother was originally included in the movie, but was cut out in the beginning of the movie's production. She eventually appeared in Shrek 2 (2004) and would form a lasting impact across the film series (this is the only film that doesn't feature her at all).
Eddie Murphy and Jeffrey Katzenberg have known each another since the beginning of their film careers. They promised that one day, they would do an animated film together, which culminated with this film. Katzenberg even recommended Murphy for the part of Donkey, and no-one else. He thinks its Murphy's best work.
In an interview once Eddie Murphy joked that the movie Shrek, and his character Donkey, became so popular that had he died the year the movie was released newspapers would have probably used a picture of Donkey instead of Eddie Murphy.
William Steig, the writer of Shrek, also wrote a Children's book called "Sylvester and the Magic Pebble" In which, a donkey has a magic pebble and, scared of a lion, wishes himself to be a boulder for protection. This is referenced in Shrek in Donkey's famous quote "I like that boulder, that is a nice boulder."
The crescent moon on Shrek's outhouse was originally going to be the DreamWorks logo moon. The studio refused; however, it can be said that Shrek's outhouse, has a crescent moon comparable to DreamWorks logo, carved into the door.
An armor expert was brought in to show the animators a variety of armors that they could use as inspiration in the film. The animators tried on the armor, studied how they moved with the armor on, and also took turns flailing different swords.
Co-director Andrew Adamson frequently found himself at loggerheads with Jeffrey Katzenberg over the film's adult jokes. Katzenberg thought that some of the more adult material was inappropriate for an animated film, Adamson disagreed. Adamson could be perceived as winning the argument as many critics liked the film for the fact that it didn't just pander to under-age audiences.
An additional scene was storyboarded but never filmed that revealed Lord Farquaad's plan for Duloc. He wanted to turn the entire kingdom into something like a gigantic shopping complex. Another scene planned and scrapped was Fiona getting Shrek and Donkey lost on the way back to Duloc.
The intent with Fiona was to create the most photorealistic CGI depiction of a human. Prior to this, people animated through CGI had a certain stiffness and the facial features remained a little blank. To this end, the animation team brought in a leading Hollywood beautician to tell them how she applied make-up to A-lister stars.
According to Andrew Adamson, Shrek's height varies between seven and eight feet depending on who you ask. He was seven feet and since then he's grown in people's minds, and now he's usually referred to as eight feet.
Shrek was almost made in stop-motion animation, but early tests proved too costly and executives weren't pleased with the overall look and lack of facial expression in the main character. After live-action miniatures and motion-capture graphics also proved unsatisfactory, the studio went with computer-generated animation.
Early concept sketches of Shrek in the 1990s saw him living in a garbage dump near a human village called Wart Creek. Another version saw him living with his parents and keeping rotting fish in his bedroom.
The list of fairytale characters in the movie: Snow White and the Seven Dwarves; the Wicked Witch of the West (or the East); The Three Bears; Pinocchio and Geppetto; the Three Little Pigs; Tinkerbell and Peter Pan; The Big Bad Wolf; The Pied Piper of Hamelin; The Gingerbread Man; Cinderella; Robin Hood and his Merry Men.
Farquaad's logo is very similar to Facebook's logo. However, this cannot be a deliberate choice by the creators of Shrek and is likely a coincidence, as Facebook and its logo were not established until 2004, three years after the film came out.
John Lithgow always said that he would never play anyone short, but he couldn't pass up the Shrek role. He believed that part of the joke of his casting was the difference between his height and his character's.
When the masked executioner, Thelonious, is singing, it is a direct reference to a "Stacker 2" commercial that the "WWF (World Wrestling Federation)" character Kane (Glenn Jacobs), who also wears a mask, appears singing karaoke.
Though Shrek bears a striking whole-body resemblance to the late wrestler and acromegelac Maurice Tillet ("The French Angel"), Dreamworks has neither confirmed or denied the rumor that Shrek was modeled on Tillet.
Nicolas Cage was initially offered the role of Shrek but he turned it down because he did not want to look like an ugly ogre. In 2013, Cage admitted that he regrets the decision, and explained: "When you're drawn, in a way it says more about how children are going to see you than anything else, and I so care about that."
When Donkey and Shrek are looking up at the stars, Shrek points out the constellation "Bloodnok the Flatulent", a reference to the character Major Bloodnok, created by Spike Milligan and voiced by Peter Sellers in the 1950s BBC Radio program "The Goon Show".
When Shrek removes his helmet after saving Fiona, revealing himself to be an Ogre, he sarcastically asks if she was expecting Prince Charming. This turned out to literally be true in Shrek 2 (2004) where Fiona's purpose for being in the tower was revealed.
One of the most difficult parts of creating the film was making Donkey's fur flow smoothly so that it didn't look like a Chia Pet's fur. This fell into the hands of the surfacing animators who used flow controls within a complex shader to provide the fur with many attributes (ability to change directions, lie flat, swirl, etc.) It was then the job of the visual effects group, led by Ken Bielenberg, to make the fur react to environment conditions. Once the technology was mastered, it was able to be applied to many aspects of the Shrek movie including grass, moss, beards, eyebrows, and even threads on Shrek's tunic. Making human hair realistic was different from Donkey's fur, requiring a separate rendering system and a lot of attention from the lighting and visual effects teams.
Radio Disney was told not to allow any ads for the film to air on the station, stating, "Due to recent initiatives with The Walt Disney Company, we are being asked not to align ourselves promotionally with this new release Shrek. Stations may accept spot dollars only in individual markets." The restriction was later relaxed to allow ads for the film's soundtrack album onto the network.
Raman Hui, supervising animator of Shrek, stated that Fiona "wasn't based on any real person." and he did many different sketches for Princess Fiona and had done over 100 sculptures of Fiona before the directors picked the final design.
In the original script Dragon was going to have hair on her head and be more overweight so Donkey's flirting with her would have been more effective but test audiences didn't like the idea so the idea was removed from the final draft.
As the film takes place in a fairy tale world, it should not be surprising that people accept without question the idea of walking mice, talking pics, ogres, and a talking puppet. It may seem strange, then, that characters are shocked to find out that Donkey can talk. One fan theory posits an answer to this. As the film is populated with parodies of Disney characters, it has been suggested that Donkey wasn't born a donkey, but was turned into one at Pleasure Island.
The original script had Princess Fiona born an ogre to the late King and Queen of Duloc. They had her locked in the tower under the lie that she was "of such rare beauty" she was kidnapped. They died, and the kingdom was left under the rule of an ambitious regent (implied to be Farquaad). When she 'became of age' to ascend the throne she escaped the tower and encounters a witch named Dama Fortuna - who has narrated the entire sequence through her tarot cards. She gave Fiona a potion which would make her beautiful; but warned her the potion had a side effect - she would change between her human and ogress form until she found her true love. Later she was whisked away by her dragon guardian and returned to the tower. This storyline was not adapted to keep the story simple, but is mentioned through the "witch" Fiona tells Donkey about.
When climbing up the fiery mountain to rescue Princess Fiona, Donkey says 'My mouth was open and everything' when Donkey thought Shrek passed wind. Eddie Murphy used the same line in his stand up comedy movie 'Delirious' (1983) when he mentioned 'You could fart in your friend's face while watching the game, he don't care...'