- “Hmmmmmmm.......No sir, I don't like it.”
- ―Mr. Horse
Mr. Horse is the most frequently recurring character in the series. He oftentimes acts as a 'bit character' carrying on many different roles, depending on the plot or the episode. He is voiced by series creator John K. who also voices Ren and several other characters. After he was fired, Billy West took over the role.
Mr. Horse is, as his name implies, a horse with a gray coating and a dark blue mane. His appearance remains overall the same, but depending on the episode or the part he is portraying, he occasionally wears clothes. In all of his appearances, he is seen with horseshoes.
He first appeared in "The Big Shot," testing out the difference between litter box A and litter box B - the Gritty Kitty formula. He first tests litter box A and replies "No sir, I don't like it" (which became his catch phrase).
He also appeared in "Rubber Nipple Salesmen" when Ren and Stimpy went to his door to sell their rubber nipples, but he was dressed in them. He believed them to be the FBI, but Ren assured them that they weren't. It is implied that he might've kidnapped a walrus, as he says that the pair can try and sell the rubber nipples to him, who whispers, "call the police."
He was a preliminary judge in "Dog Show" as if he didn't like the animal, he'd cut them out of the competition and force them to be eaten by a monstrous dog.
"In The Great Outdoors", his voice can be heard after Ren is transformed into a horse by food pills, saying his classic line, which turns out to be the final time that Mr. Horse would be voiced by Billy West, who also took over portraying most of John K.'s other roles
He and Ren appear in various episode shorts in Season 2, entitled "World Crisis With Mr. Horse" where he and Ren portray reporters.
He also made many cameos afterwards, such as at Ren's party in "Jerry The Bellybutton Elf". In the appearances after John K.'s firing that he ends up speaking, he is voiced by John K.
In "My Shiny Friend" he appears on television in The Muddy Mudskipper Show, telling Muddy not to hit him with a mallet, which he would end up doing, regardless.
In "Ren's Insomnia" he appears as one of Ren's golfing buddies. It appears in the post-Spumco era that he is close friends with Muddy, as they make a variety of appearances together.
He appears three times in the Ren and Stimpy "Adult Party Cartoon" (a.k.a. "Ren & Stimpy's All New Adult Party Cartoon"). Where he is once again portrayed by John K.
His first appearance was in Ren Seeks Help, in which he is called "Dr. Mr. Horse" and portrays a therapist that Ren goes to after his argument with Stimpy. He appears to be scared by Ren's story of his childhood and pulls out a gun for protection. After Ren confesses what he did to Stimpy, Mr. Horse calls him crazy and tries to beat him up, which leads into a fight that ends with Ren scratching Mr. Horse and beating him to death with his own gun.
Despite this, his death appears to be non-canon.
He makes a cameo appearance in Fire Dogs 2, where he and several other animals (among them Mrs. Buttloaves) wait to pee on Ren and Stimpy's fire hydrants.
His final appearance was in "Stimpy's Pregnant" where he is called Dr. Precision, who attempts to deliver Stimpy and Ren's child. He gets his name from his "precision hooves". He continuously beats the nurse, and scolds Ren for hitting Stimpy during the delivery. After taking a look at Stimpy's X-ray, he realizes that Stimpy is merely constipated, but to avoid breaking their hearts, he delivers the 'child' (which turns out to be excrement) and molds it into a human baby, which becomes sentient.