Stimpson J. Cat, better known as Stimpy, is the deuteragonist of The Ren & Stimpy Show and the APC version.
Stimpy is a red and white, rotund manx cat with a blue nose, purple eyelids, no tail, hands with gloves that have fingernails, human-style buttocks, flat feet, and a brain the size of a peanut (despite some intelligence, such as cooking and inventing; and has some other knowledge such as monetary counting and knowing that pork fat floats on beans).
Stimpy is a kind-hearted, dim-witted, simple-minded, good-natured cat who constantly makes Ren mad with his stupidity, who in retaliation hits Stimpy, sometimes saying "you eediot!". Martin "Dr. Toon" Goodman of Animation World Magazine described Stimpy as "obese," and "brain-damaged." Andy Meisler of The New York Times described Stimpy as "bosom," "barrel-chested," and "good-natured."
Stimpy's trademark facial expression is a blissfully ignorant smile with his tongue flopping out. Most of the time when he gets excited, he says his famous catchphrase, "Oh, joy!" or simply "Jooooooy".
Stimpy likes to create destructive electronic devices and feels a fixation for, in the words of Andy Meisler of The New York Times, "sensory pleasures of fresh kitty litter." Wray described Stimpy as his favorite character to draw. Wray said that Stimpy does not have "a huge range of emotion." West said in an interview that he did not wish to voice Stimpy in the Adult Party Cartoon because he believed that the series was not funny and that voicing Stimpy in it would damage his career.
- Stimpy is named after an art school classmate of Kricfalusi, whose nickname was "Stimpy Cadogen" ("Killer Cadoogen" was Stimpy's pseudonym in several episodes, and in a few others he is referred to as Stimpleton Cadogen).
- John K. prided himself on keeping Ren & Stimpy animation style inconsistent, meaning there is no default appearance for Stimpy.
- West said that he based Stimpy's voice on a "sped up" Larry Fine of the Three Stooges. West described Stimpy as one of his favorite characters.
- Eric Bauza voiced Stimpy in Ren & Stimpy "Adult Party Cartoon" and Nicktoons MLB.