Dr. Jacques von Hämsterviel is a diminutive, rodent-like alien scientist with white fur and red eyes. His features blend gerbil and rabbit traits, including long ears, buck teeth, and a bushy-tipped tail. Though he insists he is "hamster-like," others often mistake him for gerbil-like or rat-like. He constantly wears a distinctive red cape fastened with a golden "H" brooch, even over a striped prison jumpsuit during incarceration. His background involves being the former partner of Dr. Jumba Jookiba. Together, they founded "Jokes on You" after graduating from Evil Genius University. Their partnership shifted to creating illegal genetic experiments, with Hämsterviel financing their work through unspecified "shady business practices" while Jumba handled design and engineering. Hämsterviel betrayed Jumba by informing the Galactic Federation, leading to Jumba's arrest. Hämsterviel was later imprisoned himself; Jumba initially thought him dead. After escaping prison, Hämsterviel relentlessly pursued reclaiming the experiments, believing his financial backing made them his property. Hämsterviel exhibits a Napoleon complex, compensating for his small size with grand ambitions of galactic domination and extreme self-absorption. He displays ruthless cunning, frequently insulting and berating subordinates like Captain Gantu, whom he re-hires as a henchman. Despite Gantu's loyalty, demonstrated by aiding his prison escapes, Hämsterviel callously dismisses him when deemed obsolete, replacing him with Leroy clones. This treatment ultimately drives Gantu to betray him, contributing to his defeats. He harbors intense animosity toward Jumba, Stitch, Lilo, and Pleakley, constantly scheming to enslave or eliminate them. Paradoxically, he reveals cowardice when directly confronted with physical threats, such as being trapped in his own laser-cutting device or facing vengeful experiments alone. His schemes evolve across different media. Initially, he operates from a technologically equipped prison cell, hiring Gantu to capture Jumba's experiments for conquest, manipulating events in *Stitch! The Movie* and *Lilo & Stitch: The Series*. In *Leroy & Stitch*, he forces Jumba to create Leroy, clones an army, and temporarily overthrows the Galactic Council before defeat and re-imprisonment. In the *Stitch!* anime continuity, he partners with the alien Delia to capture Stitch, aiming to extract a power cell for a new experiment. He also steals existing experiments from the Galactic Federation and Hawaii, using transmutation technology to "re-evil" them, enhancing their abilities and ensuring obedience. Additionally, he creates his own experiment, Skunkuna, to cause destruction. In *Stitch and the Planet of Sand*, he continues pursuing intergalactic power. His broader modus operandi involves exploiting experiments and allies for conquest, consistently failing due to underestimating opponents and alienating supporters. Following defeats, he is frequently shown imprisoned but unrepentant, depicted tapping his foot petulantly while surrounded by captured Leroy clones. A recurring trait is his irritation at mispronunciations of his name, such as "Hamsterwheel" or "Hamsterveal," reflecting his desire for recognition. His accent ambiguously blends French ("Jacques") and German ("Hämsterviel"), though adaptations like the German dub alter his name to "Dr. Hans van Hamsterdam," implying Dutch origins.