Shrek cracks a mirror by looking into it and smiling: the scene is virtually identical to the same one featured in Mike Myers' Austin Powers films.
Donkey's line "I had my mouth open and everything" actually came from part of Eddie Murphy's "Delirious" routine.
And the line "I'm a donkey on the edge!" may be a reference to 48 Hrs.:
"I am your worst nightmare! A nigga with a badge!"
Shrek tells Donkey "You're going the right way for a smacked bottom". Austin Powers said the exact same thing to Madonna in the Beautiful Stranger video. Funnily enough, this wasn't even a planned reference. According to the DVD commentary, Mike Myers said the line in jest to a crew member at one point when he was frustrated about something or other- and they decided to go ahead and Throw It In!.
Actor-Inspired Element: Mike Myers originally voiced Shrek with a roughed-up version of his real Canadian accent (which can be heard in some of the outtakes included on the DVD and Blu-ray). However, he was unsatisfied with the finished performance and asked to rerecord the whole thing. This time he based the ogre's voice on his parents' Scottish accents- and thus Shrek became the Scotsogre we all know and love.
In the Brazilian dub, comedian Bussunda was Shrek. When he died in 2006, The Other Darrin was also The Other Marty: professional dubber Mauro Ramos, whose already recorded track for the first movie served as reference for Bussunda's performance, took over the role in the movies and specials that followed.
Creator Killer: Not to DreamWorks itself, but one of the franchise's sources of fuel was all the snark, bitterness and derision directed towards Disney boss and Katzenberg's former superior Michael Eisner, including having Farquaad be a caricature of him; this movie was one of the multiple punches that eventually knocked Eisner out of the Mouse House in 2005 (nearly losing Pixar was the final punch to send him to the floor).
Cross-Dressing Voices: Gingy is puppeteered and voiced by a woman in each production of Shrek the Musical. Averted in foreign dubs of the film.
One from the first film has Fiona meeting a Gypsy woman named Bib Fortuna (a reference to the Star Wars character of the same name), who would eventually become the Fairy Godmother. In this version Fiona is always an ogre, and Bib Fortuna gives her a potion that would make her beautiful, but tells her that she will alternate between her human and ogress forms until she finds true love. After that, she is whisked away by her dragon guardian and returned to the tower.
There was going to be a scene shortly after Shrek and Donkey get Fiona out of the dragon's keep that would involve them riding a mine cart like a roller coaster, complete with at least three references to Disneyland via the talking skull from Pirates of the Caribbean, the yeti from Matterhorn Bobsleds, and the Country Bears. The storyboards for this scene are included in the DVD.
After Shrek won the tournament in the first film, there was to be a scene where Farquaad explains the quest to Shrek and they're standing side-by-side to show their size comparison (explaining Shrek and Donkey's size jokes to Fiona later in the film). Several ideas for that scene include them walking by a garden or having dinner. One was storyboard in which Farquaad shows Shrek and Donkey his desire to turn Duloc into a more modern city with convenient stores and mini-malls, and it shows Farquaad holding the deed to the swamp.
Development Hell: The fifth movie has gone through a prolonged development cycle which has repeatedly stalled. Originally intended for a 2013 release date after Shrek the Third, the latter movie's poor critical reception caused plans for the fifth movie to get cancelled, with Shrek Forever After becoming the series' Grand Finale as a result. The movie's production since restarted in 2016, but has since been repeatedly delayed with no concrete release date in sight and rumors waffling on whether it's actually the fifth movie or an outright Continuity Reboot.
It's difficult to imagine just how influential and popular Shrek was when it first came out, as just about every western animated feature has been influenced by its humor and style, not to mention "proving" that computer animation was the only way to go in the 21st century. In a nutshell, the trend was for such a film to star talking animals voiced by celebrities and featuring pop-culture references and body/toilet humor, i.e. Ice Age, Open Season, etc.
After the first film became a roaring success, it would take nearly a decade for non-ironic fairy tale movies, especially ones made by Disney, to be taken seriously again. It didn't help that, in the decade preceding Shrek, Disney had done nothing but blockbuster musicals, mostly with princesses and princes, following the box office underperformance of The Rescuers Down Under (which Katzenberg oversaw) and some of Disney's staff were losing interest in it at that point themselves, as evidenced by The Emperor's New Groove being a full-blown comedy and Atlantis: The Lost Empire being an adventure film.
Along with Blue Sky Studios' Ice Age, another hugely successful non-Disney CGI filmnote Disney would ironically obtain the rights to that film upon buying 20th Century Fox (Blue Sky's parent company) in March 2019, it wound up being the final nail in the coffin for hand-drawn feature film animation in America, which had been on a slow decent in popularity for the later half of the 90s. Dreamworks would close it's 2D animation unit in 2003 and Disney would follow suit a year later, allowing the last few 2D movies they'd produced to die a quick, painless death at the box office so they could jump on the CGI bandwagon as quickly as possible. Despite some conceited efforts to keep the art form alive in the late 2000s/early2010s, CGI has remained the standard for all American animated features ever since.
The Other Marty: Chris Farley was attached to Shrek early in its development, but after his death (and many story changes) the role went to Mike Myers, who then performed an odd same-actor version of this trope, switching to a Scottish accent partway through and re-recording already-done lines.
Permanent Placeholder: According to Word of God, the use of the Smash Mouth song "All Star" at the beginning of the first movie was only intended as test footage track to get the timing of the opening down - they planned to use an original composition for the final product. However, "All Star" worked so well that they kept it in.
Serendipity Writes the Plot: You'll notice that both times we visit the city of Duloc, the streets are completely empty and deserted. The crowd scenes were specifically written to take place indoors or in another confined location to save on rendering costs for large groups of characters all moving independently of one another.
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.
The line "Can't we just settle this over a pint?" was something the producers actually said to Myers to convince him to join the film. They threw it into the script after he agreed.
The scene where Princess Fiona burps was written after Cameron Diaz burped during a recording session after drinking Coca-Cola. Donkey's quip, "She's just as nasty as you are!" was what Eddie Murphy actually said to Myers in response.
The film was originally going to be produced by Steven Spielberg, be hand-drawn (and later on, motion-captured), and star Bill Murray as Shrek and Steve Martin as Donkey. Spielberg did however still serve as the executive producer for the film, albeit going uncredited.
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.
Originally, Shrek was driven out of his swamp by Farquaad's guards who burned his house down. The filmmakers thought, although it was dramatic, it wasn't funny (like the scene we got in the finished film).
Chris Farley was originally cast as Shrek and even recorded some dialogue. When Farley died, another SNL cast member got his part (Mike Myers). Initial reports were that the script was radically reworked after Farley's death and Myers was basically voicing a different character. However, this was proven false when a recording of Farley as Shrek was unearthed with dialogue largely similar to a scene in the finished film.
Myers himself was initially hesitant about accepting the role because he was friends with Farley and didn't want to disrespect his memory. He changed his mind after thinking it over.
Janeane Garofalo was originally going to voice Fiona, but with the recasting of Shrek's voice actor, Fiona's voice and character were changed so she could contrast with Shrek better.
Supposedly, Robin Williams was approached for a role, but because of the bitter falling out he had with Jeffrey Katzenberg after the latter breached Williams's contract stipulations for Aladdin, he refused to work on this or any DreamWorks film.
An IMAX 3-D version that would have added an alternate ending was also planned to be released in either December 2001 or summer 2002, but was cancelled.
In the first movie, they wanted the crescent moon on Shrek's outhouse to be the DreamWorks logo moon. But the studio said no.
Shrek originally looked quite goofy◊ (it's the picture on the right).
Writer Revolt: Well, producer revolt. Former Disney CEO Jeffrey Katzenberg made this film as a great big "Screw you!" to his previous company and especially his former partner Michael Eisner, whom he loathed, after Eisner shot down many of Katzenberg's idea and later beat him out of the studio head position. It worked, seeing as how this film put DreamWorks on the map and ended up indirectly contributing to Eisner being let go by Disney.
What Could Have Been: The Pocket Shrek app was meant to have Fiona as an interactable character alongside Shrek, Donkey and Puss and even got advertised in-game, but she was cancelled when the app went offline and stopped receiving support.