- "Behold, the Underminer! I'm always beneath you, but nothing is beneath me! I hereby declare war on peace and happiness! Soon, all will tremble before me!"
- —The Underminer
The Underminer appears at the end of the movie, where he announces his "war on peace and happiness!" The Parr family then put on their masks, ready for battle. This led to such a cliffhanger that the creators of the original Incredibles video game created the sequel, The Incredibles: Rise of the Underminer.
The Underminer returns in the opening sequence of the movie, picking up the story where the first Incredibles movie left off. Violet's date ends up seeing Violet in her super-suit without her mask on, which causes a bit of an uproar in the Parr family. The Underminer uses his drill to wreck havoc on the city and to rob the town bank using a device that functions like a vacuum. Mr. Incredible attempts to face off against the Underminer but is sucked up by the Underminer's vacuum and into a vault in the Underminers drilling rig. The Underminer attempts to make his escape but Mr. Incredible manages to escape the vault and fight the Underminer. During the fight the drill's controls are destroyed and it begins to resurface. The Underminer makes his escape using an escape pod leaving Mr. Incredible to deal with the out of control drill machine. The resulting aftermath of the drill machine almost destroying City Hall and the Underminer escaping results in Supers being outlawed and the relocation program shut down. The Underminer isn't seen for the rest of the film.
- Brad Bird had stated in the commentary that John Ratzenberger having a part in every film was a Pixar tradition that he was originally not planning to use. However, he did end up giving Ratzenberger a part, with the joke being that his voice is the very last thing viewers hear in the film.
- He appears to have robotic prosthetic hands. They seem to be incredibly strong, with a punch from them knocking Mr. Incredible off balance and even capable of catching his punch with little effort.