Ren Höek is a hot-tempered, "asthma-hound" Chihuahua. Kricfalusi originally voiced Ren, styled as a demented Peter Lorre. When Nickelodeon fired Kricfalusi, Billy West, already the voice of Stimpy, took the role using a combination of Burl Ives, Kirk Douglas and a slight "south of the border accent" for the rest of the Nickelodeon run. Stimpson "Stimpy" J. Cat is a three-year-old dim-witted and happy-go-lucky cat. West voiced Stimpy for the Spümcø and Games Animation episodes, basing the voice on an "amped-up" Larry Fine.
Ren and Stimpy play various roles, from outer-space explorers to Old West horse thieves to nature-show hosts, and usually the duo were constantly at odds with each other. While the show was sometimes set in the present day, the show's crew tended to avoid "contemporary" jokes that reference current events.
The show features a host of supporting characters; some only appear in a single episode, while others are recurring characters, who occasionally appear in different roles. Some of the supporting characters factor directly into the storyline, while others make brief cameos. Other characters, such as Mr. Horse, are exclusively cameo-based, appearing in many episodes in scenes that have little bearing on the plot, as a running gag. Some notable artists and performers who voiced incidental characters on the show are Frank Zappa, Randy Quaid, Gilbert Gottfried, Rosie O'Donnell, Dom DeLuise, Phil Hartman, Mark Hamill, Alan Young, Frank Gorshin and Tommy Davidson.
The show's pilot began production in 1989, after Kricfalusi pitched and sold The Ren & Stimpy Show to Nickelodeon. The pilot was done by Kricfalusi's own animation company, Spümcø, and screened at film festivals for several months before the show was announced in Nickelodeon's 1991 line-up. The first episode of the show premiered on August 11, 1991 alongside Doug and Rugrats. Spümcø continued to produce the show for the next two years while encountering issues with Nickelodeon's Standards and Practices. The show was noted for its lack of early merchandising; Wray cites the initial lack of merchandise as "the unique and radical thing" about The Ren & Stimpy Show, as no toy company planned ahead for any merchandise for the show, and Nickelodeon did not want to use "over-exploitive" merchandising.
Kricfalusi described his early period with Nickelodeon as being "simple", as he got along with Coffey, the sole executive of the program. When another executive was added, he wanted to alter or discard some of the Ren & Stimpy episodes, but Kricfalusi says the episodes stayed intact since he did a "trade" with Coffey: he would have some "really crazy" episodes in exchange for some "heart-warming" episodes. According to Kricfalusi, The Ren & Stimpy Show was the "safest project [he] ever worked on" while explaining the meaning of "safe" as "spend a third of what they spend now per picture, hire proven creative talent, and let them entertain". He estimated Spümcø's run of The Ren & Stimpy Show cost around $6,000,000 to produce.
The show received mixed reviews. Terry Thoren, former CEO and president of Klasky Csupo, said that Kricfalusi "tapped into an audience that was a lot hipper than anybody thought. He went where no man wanted to go before – the caca, booger humor". The Morning Call called it "high voltage yuks and industrial-strength weirdness". Even as the show came to garner high ratings for Nickelodeon and developed a cult following, the relationship between Kricfalusi and Nickelodeon became strained, eventually leading to Kricfalusi communicating with Nickelodeon solely through his lawyer. Several of the show's staff and news sources attribute the tension to episodes not being delivered in a timely manner. Andy Mangels of Wizard magazine commented that "Kricfalusi's lax treatment of deadlines pissed off not only the networks, but his loyal viewers as well." However, some of the delays were attributed to Nickelodeon's prolonged approval process and withdrawal of approval from scenes and episodes that had been previously approved. Another issue of contention was the direction of the show. Nickelodeon later asked the new studio to make it lighter and less frightening. Kricfalusi cites the primary reason for his dismissal as the episode "Man's Best Friend", which features a violent climax where Ren brutally assaults George Liquor with an oar.
The show's aesthetics draw on Golden Age cartoons, particularly those of Bob Clampett in the way the characters' emotions powerfully distort their bodies. The show's style emphasizes unique expressions, intense and specific acting, and strong character poses. One of the show's most notable visual trademarks is the detailed paintings of gruesome close-ups, along with the blotchy ink stains that on occasion replace the standard backgrounds, "reminiscent of holes in reality or the vision of a person in a deep state of dementia". This style was developed from Clampett's Baby Bottleneck, which features several scenes with color-cards for backgrounds. The show incorporated norms from "the old system in TV and radio" where the animation would feature sponsored products to tie in with the cartoon, however in lieu of real advertisements, it featured fake commercial breaks advertising nonexistent products, most notably Log.
Carbunkle Cartoons, headed by Bob Jaques and Kelly Armstrong, is credited by Kricfalusi for beautifully animating the show's best episodes, improving the acting with subtle nuances and wild animation that could not be done with overseas animation studios. Some of the show's earlier episodes were rough to the point that Kricfalusi felt the need to patch up the animation with sound effects and "music bandaids," helping the segments "play better, even though much of the animation and timing weren't working on their own." KJ Dell'Antonia, a reviewer for Common Sense Media, describes the show's style as changing "from intentionally rough to much more polished and plushie-toy ready."
The Ren & Stimpy Show features a wide variety of music, spanning rockabilly, folk, pop, jazz, classical music, jingles, and more. The opening and closing themes are performed by a group of Spümcø employees under the name "Die Screaming Leiderhôsens". Three Ren & Stimpy albums have been released: Crock O' Christmas, You Eediot!, and Radio Daze. In addition to music written specifically for the show, a number of episodes utilized existing works by composers such as jazz musician Raymond Scott, Debussy, Tchaikovsky, Beethoven, Alexander Borodin, Antonín Dvořák, Rossini (particularly The Thieving Magpie), and a host of "production music" by composers such as Frederic Bayco, which fans later compiled into several albums. In 1993 a compilation album, "You Eediot!", was released as a soundtrack album. The album's front cover is a parody of The Beatles' 11th studio album Abbey Road.
Stimpy's rousing anthem titled "Happy, Happy, Joy, Joy" was composed by Christopher Reccardi and written by Charlie Brissette and John Kricfalusi. A cover of this song, performed by Wax, is included on the 1995 tribute album Saturday Morning: Cartoons' Greatest Hits, produced by Ralph Sall for MCA Records. The line "happy, happy, joy, joy" is first used in episode three of the series; the song is first played in episode six. It is sung by a character introduced as "Stinky Whizzleteats", who is named in the episode's script as Burl Ives. Several references to Burl Ives's songs and movie quotes are sprinkled through the song, giving it its surreal air.[talk]
The series ran for five seasons, spanning 52 episodes. The show was produced by Kricfalusi's animation studio Spümcø for the first two seasons. Beginning with season three (1993–1994), the show was produced by Nickelodeon's Games Animation. The episode "Man's Best Friend" was produced for season two, but the episode was shelved and debuted with the show's adult spin-off. Another episode, "Sammy and Me / The Last Temptation", aired on MTV on October 20, 1996, almost a year after the original Nickelodeon run ended.