Dr. Jacques von Hämsterviel, occasionally localized as Dr. van Hamsterdam in regional adaptations, serves as a central antagonist in the *Lilo & Stitch* franchise. He shares a history as both partner and co-graduate of Evil Genius University with Dr. Jumba Jookiba. Initially, they operated a venture named "Jokes on You" before collaborating on illegal genetic experiments—Jumba provided scientific expertise while Hämsterviel funded operations through unspecified illicit dealings. Hämsterviel later betrayed Jumba by alerting the Galactic Federation during Experiment 626's (Stitch's) creation, causing Jumba's arrest. Though subsequently imprisoned himself, Hämsterviel was presumed dead by Jumba until later encounters. Physically, he manifests as a diminutive rodent-like alien with white fur, red eyes, a rabbit-like face, long ears exposing pink innards, buck teeth, a triangular pink nose, a cow-like tail tipped in bushy brown fur, and a gerbil-like lower body. He typically wears a red cape secured by a golden "H" brooch. Despite insisting he resembles a hamster, observers frequently mistake him for gerbil-like or rat-like. He exhibits acute sensitivity to mispronunciations of his name (such as "Hamsterwheel" or "Hamsterveal") and species misidentification. His personality hinges on extreme megalomania and a Napoleon complex, driving an obsessive pursuit of galactic domination. Arrogant and self-absorbed, he deems no one his equal and habitually insults associates like Jumba and his henchman Captain Gantu. He subjects Gantu to relentless verbal abuse and physical assaults, demonstrating zero loyalty by discarding minions after their usefulness expires—culminating in Gantu's dismissal post-Leroy's creation. Beneath his bluster, Hämsterviel reveals cowardice when overpowered, resorting to pleading or claiming his actions were jokes. Flashbacks depict a more jovial demeanor during his early partnership with Jumba. His narrative initiates in *Stitch! The Movie*, where he hires imprisoned Gantu to kidnap Jumba and steal the remaining 625 experiments, asserting ownership via prior financing. His scheme to dissect Stitch collapses, resulting in re-arrest after experiments scatter across Earth. Throughout *Lilo & Stitch: The Series*, he orchestrates plots from prison via communication screens, berating Gantu for failures and briefly escaping to become the temporary pet of Lilo's rival, Mertle. In *Leroy & Stitch*, Gantu aids his prison escape. He coerces Jumba into creating Experiment 629 (Leroy), a red, enhanced Stitch clone, then mass-produces Leroys to overthrow the Galactic Federation. After seizing temporary control, he fires Gantu—prompting Gantu to ally with Lilo and Stitch against the Leroy army. Defeated, Hämsterviel is re-imprisoned on Asteroid K-37, Cell 750. Later, in *Stitch!* anime season three, he partners with a formidable alien, Delia. Stealing experiments from the Galactic Federation and Hawaii, he deploys methods like Angel's song or DNA transmutation to revert them to evil under his command. His primary goal shifts to capturing Stitch to harness his Powersurge—a natural battery amplifying abilities—to forge a new super-experiment. He also engineers his own creation, Skunkuna, to unleash chaos.