Kricfalusi received inspiration, used when drawing the first drawings of Ren, from a Elliott Erwitt black and white photograph of a growling chihuahua in a sweater next to a woman's feet.
Billy West also auditioned to play Ren but the creators of the series believed that having West voice both Ren and Stimpy would give him too large of a workload, as he also voiced the titular character of Doug. So Kricfalusi voiced him instead.
It is implied several times that Ren may be older than Stimpy, perhaps by a large margin. This is supported by how in Ren's Retirement, Ren is stated to be ten - 70 in dog years - while Stimpy is said in "Stimpy's Big Day" to be three - 21 in cat years. In "I Was a Teenage Stimpy" Stimpy was shown to go through puberty, with Ren taking on the role of a conservative father to him, being happy that once Stimpy 'grew up' he'd have somebody to take care of him.
In Adult Party Cartoon, Ren's voice is deeper in an attempt to make him sound older, perhaps a reference to this.
The origin of the gag of Ren being referred to as a 'mosquito' could've been inspired by how many of the cast and crew members had at first believed him to be a fly or a mosquito after seeing his concept art.
His and Stimpy's appearances in the Stephen Squirrelsky and Friends' movie spoof travels are The Great Hedgehog Detective (FamousImagination50's Style), The Sword in the Stone (Stephen Druschke's Animal Style), Vanellope Von Schweetz (a.k.a. Pippi Longstocking), The Train and the Boat, Toon Age (J.B. Eagle's Style), Cub and Company, Happily Ever After (Stephen Druschke's Style), Hoodwinked! (Dalmatian Tunes' Style), Beauty and the Grizzly Bear, The Rescuers (TrainBoy43's Style), Nikki's Adventures of Sing Along Songs Episode 4, The Rescuers Down Under (TrainBoy43's Style), The Secret of NIMH (Nikkdisneylover8390's Human Style), Nikki's Adventures of Sing Along Songs Episode 6, The Little Mer-Lioness II: Return to the Sea, Skunkules, Home on the Range (DalMatian Tunes' Style), Kermit's Winter Wonderland, The Little Jungle Boy, Kermiladdin 2: The Return of McLeach, AiAi the Monkey and A Day for George, The Reindeer and the Deer, Animal Story 2 (Stephen Druschke's Style), AiAi's Grand Adventure: The Search for Tails, A Cartoon Character's Life, Nikki's Adventures of Sing Along Songs Episode 7, Here Comes Winnie the Pooh, Animals, Inc. (Dragon Rockz's Style), Simba 2, Miss Bianca and the Bernard 2: Fievel's Adventure, FernGully: The Last Rainforest (Dragon Rockz's Style), A Pooh in Central Park, Bubblesrella 2: Dreams Come True, Kung Fu Owen, Nikki's Adventures of Sing Along Songs Episode 8, The Thomas O'Malley Movie, Kermit Returns, Fievel the Red Nosed Mouse and The Island of Misfits, Nikki's Adventures of Sing Along Songs Episode 9, A Cartoon Character's Life Activity Center, Cloudy with a Chance of Meatballs (Justin Quintanilla's Style), Finding Alvin (J.B. Eagle's Style), Animated Tale (TheTure DisneyKing's Style), The Forest Book 2 (TrainBoy43's Style), Nikki's Adventures of Sing Along Songs Episode 10, Madagascar (FamousImagination50's Style), Sleeping Beauty (Justin Quintanilla's Style), Aurorastasia, Despicable Me (Justin Quintanilla's Style), We're Back!: A Jungle Animal's Story, Jimmynocchio, and The Wizard of Oz (Uranimated18's Style) and will even be in more movie spoof travels.
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