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.
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.
The song "All Star" by Smash Mouth, heard in the opening credits, was only a placeholder for test screenings 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 perform the last song in the movie, "I'm a Believer."
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 $4 million, 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.
Shrek received his own star on the Hollywood Walk of Fame.