Zappa In Ren & Stimpy Show As "The Pope"

In Ren & Stimpy show Zappa presented the voice for "The Pope" (episode "Powdered Toast Man") As outlined by IMDB.com, it was the final time he would ever represent a fictional character.

Ren & Stimpy show with FZ

Harry Andronis was audio mixer on the Ren And Stimpy show and he also worked with FZ. He informed the show's director, John Kricfalusi, that FZ was a follower of the show and organized for them to meet. 

Kricfalusi on the audio commentary on the DVD version of the episode:

"Yeah, Frank Zappa was a fan of the show, and I was a huge Frank Zappa fan growing up. I had all his records. and when I found out he was a fan, our mixer, one of the sound engineers, was also mixing some frank zappa records and he uh handed the phone to me one day and it was Frank on the line. So frank invited me to his house that weekend and I went with Eleanor Blake with Frank and his family, Moon Unit and Dweezil. We all sat around watching Ren & Stimpy cartoons all afternoon he was laughing all through them and after it was over I asked: "Hey Frank, you want to be in a cartoon?' and he said: "Yeah, that'd be great." and I said: "You want to be the pope?" and he said: "Yeah, I always wanted to be the pope."

A second fascinating relationship between Zappa and the show: There was a repeating Ren & Stimpy part called “Ask Dr. Stupid” where Stimpy would react to letters in an extremely foolish way. Turns out, Zappa recorded a track known as “Ask Dr. Stupid” all the way back in 1979.

The Ren & Stimpy Show was controversial for its off-color humor, sexual innuendo, and aggression which were uncommon for TV animation of the time. The show ran for five seasons on the network, got critical acclaim, and created a cult following throughout and after its run

Certain pieces of the show were altered to prevent references to religion, politics and alcohol. The episode "Powdered ToastMan" had a cross removed from the Pope's hat and the credits transformed to "the man with the pointy hat". The same episode had a segment featuring the burning of the United States Constitution and Bill of Rights which was extracted, while in another episode the last name of the character George Liquor was removed.

A few other notable artists and performers who voiced incidental cartoon figures on the show are Randy Quaid, Gilbert Gottfried, Rosie O'Donnell, Dom DeLuise, Phil Hartman, Mark Hamill, Alan Young, FrankGorshin and Tommy Davidson.