The story begins when a police beagle is accidentally kidnapped to be a guinea pig by Capitol City's best geneticist Simon Bar Sinister (Peter Dinklage), who is secretly experimenting on dogs to perfect his serum. However, the beagle escapes, but not before causing a lab fire and being exposed to various substances. Found by ex-police officer and widower Dan Unger (James Belushi), the beagle is named "Shoeshine" and becomes the pet of Dan's 12-year-old son, Jack (Alex Neuberger). But as both eventually learn, the incident at the lab has not only made Shoeshine able to speak, but also able to fly and possess supercanine strength. Jack convinces Shoeshine to use his superpowers to help the citizens of Capitol City, taking the name, "Underdog". However, Bar Sinister (whose face was badly disfigured when a burning television monitor fell on him, during the lab fire), hunting Underdog and eventually learning of his identity, manages to get a sample of his DNA that the scientist uses on Shoeshine to turn him back to a normal dog. After feeding three DNA pills to his German Shepherds, Bar Sinister takes the mayor hostage while setting up a bomb on top of city hall, which is filled with a formula that makes whoever breaths it obey Barsinister. However, Shoeshine manages to regain his powers by eating the same pills Bar Sinister gave to the German Shepherds, afterward he turns them against Bar Sinister and saves the day.
- Jason Lee as Underdog / Shoeshine the Dog
- Peter Dinklage as Dr. Simon Bar Sinister
- Patrick Warburton as Cad Lakey
- John DiMaggio as Supershep / The Bulldog
- Phil Morris as Maim the Dog ("Supershep #1")
- Michael Massee as Kill the Dog ("Supershep #2")
- Cam Clarke as Attack the Dog ("Supershep #3") / The Little Brown Dog
- Amy Adams as Sweet Polly Purebred the Dog
- Brad Garrett as Riff Raff the Dog
- Jess Harnell as The Astronaut
- James Belushi as Daniel "Dan" Unger
- Alex Neuberger as Thomas "Jack" Unger
- Taylor Momsen as Molly
- John Slattery as The Mayor
- Samantha Bee as Principal Helen Patterson
- Jay Leno as Himself
- Stephen James Kidd as The Hot Dog Vendor Customer / The Bomb Squad Captain
The bulk of the visual effects work on the film was completed by two London-based companies, Frame Store CFC, and Cinesite. The visual effects supervisor at Cinesite was Ben Shepherd, and the animation supervisor was Alexander Williams.
Underdog was released on August 3, 2007, in 3,013 theaters across the US. It grossed $11,585,121 on its opening weekend, placing in third among that weekend's films in release. As of October 11, 2007, Underdog made $42,937,703 at the domestic box office.
Upon its release, Underdog received largely negative reviews. Rotten Tomatoes' freshness rating for Underdog stood at 15% in March 2010, the lowest of three of director Du Chau's movies at that time (Quest for Camelot and Racing Stripes, receiving 35% and 34% respectively). The movie consensus on that site reads:
"Underdog is a mostly forgettable adaptation that relies far too heavily on recycled material and sloppy production."
Ken Fox of TV Guide said: "If you set your expectations just low enough, or are an easily satisfied 8-year-old, you might have a bit of fun." The New York Daily News saw Underdog as being "made for the Saturday morning TV crowd," claiming that "parents who lead their tykes to this adventure aren't likely to leave disappointed."
Underdog was released on standard DVD and high-definition Blu-ray Disc on December 18, 2007. The DVD and Blu-ray Disc both aspect ratios with Widescreen and Fullscreen.
The DVD shows the first episode of Underdog on the bonus features.
The merchandise for the film was released on July 31, 2007 at the Disney Store. Among the merchandise released that day was a Underdog: Original Soundtrack|soundtrack album from Hollywood Records and books from Disney Publishing Worldwide. A video game was originally going to be released for Xbox 360 and PlayStation 3, but was canceled.
- This is the seventh Disney film to be based on a cartoon TV show that was non-Disney before, the first six being Popeye, George of the Jungle, Mr. Magoo, My Favorite Martian, Inspector Gadget, and The Lone Ranger.