The principal actors never met each other. 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 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, and had Mike Meyers read the line in the back of a limo.
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."
Chris Farley was originally cast as Shrek and even recorded part 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.
Mike Myers recorded Shrek's voice in a natural accentless voice before the film was test-screened. After watching it, he decided that the voice didn't sound right and had all of his lines re-recorded with a Scottish accent, based on the voice his mother used when reading him bedtime stories as a child.
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 the studio 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 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 3 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.
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 Shrek. Katzenberg even recommended Murphy for the part of Donkey, and no-one else. He thinks its his best work.
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.
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.
According to director, Andrew Adamson, Shrek's height varies between seven and eight feet depending on who you ask. He was 7 feet and since then he's grown in people's minds, and now he's usually referred to as 8 feet.
Early sketches of Shrek saw him living in a garbage dump near a human village called Wart Creek. Another version saw him living with his parents and kept rotting fish in his bedroom. These sketches were done in the mid '90s.
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".
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-animation.
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.
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 trivia items below may give away important plot points.
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 Bib Fortuna (a reference to the Star Wars character of the same name) - who has narrated the entire sequence through her tarot cards. She gave Fiona a potion which would make her beautiful; but Fortuna warns her the potion has a side effect - she will change between her human and ogress form until she finds 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.
Although Fiona's appearance was based off of Cameron Diaz, her ogre form and more specifically her facial features were based on a Dreamworks employee at the time by the name of Fiona who also had long red hair.