Runt is extremely dimwitted, believing from the time Rita met him that she was another dog. This is largely to Rita's advantage, since he would behave hostilely towards any cats.
Despite his simple mind, he has great affection for Rita, letting her insults and disdain slide off of him. Runt (usually) intermediately expresses worry and stress when he thinks she is in danger. He even went to the point of biting a man who was trying to cook Rita, and grabs her by the scruff to safety when he assumes they are in danger (although usually incorrectly, to Rita's annoyance). He is also, in his rare moments of coherency, surprisingly attached to Rita, but when she is about to leave on a train to a nice home and he is left behind, he seems sad. However, Rita quickly jumps off the train, much to his surprise and delight.
Appearances outside of Rita and Runt are italicized
Runt's voice is Welker’s impression of Dustin Hoffman's character from Rain Man.
Peter Hastings auditioned for Runt.
Runt can often show he has some of Rita's big traits. Though he usually sticks to standing on his four legs. In Phranken-Runt, Witch One and Wakko's Wish, he stands on his hind legs and acts around it the way Rita does. Runt can even sing, as shown in Les Miseranimals and Of Nice and Men
Season 2: "Take My Siblings Please / The Mindy 500 / Morning Malaise" • "Miami Mama-Mia / Pigeon on the Roof" • "We're No Pigeons / Whistle Stop Mindy / Katie Ka-Boom: The Broken Date" • "I'm Mad / Bad Mood Bobby / Katie Ka-Boom: The Blemish / Fake" Season 3: "Super Strong Warner Siblings / Nutcracker Slappy / Wakko's New Gookie / A Quake, a Quake!" • "Variety Speak / Three Tenors and You're Out / Bingo" • "Deduces Wild / Rest in Pieces / U.N. Me" • "A Hard Day's Warner / Gimme a Break / Please Please Please Get a Life Foundation" • "The Tiger Prince / All The Words in the English Language / The Kid in the Lid / Method to Her Madness" • "The Presidents Song / Don't Tread on Us / The Flame Returns" • "Gimme the Works / Buttons in Ows / Hercules Unwound" • "This Pun for Hire / Star Truck / Go Fish / Multiplication Song" • "The Sound of Warners / Yabba Dabba Boo" • "My Mother the Squirrel / The Party / Oh! Say Can You See / The Twelve Days of Christmas Song" • "Dot's Entertainment / The Girl with the Googily Goop / Gunga Dot" • "Soccer Coach Slappy / Belly Button Blues / Our Final Space Cartoon, We Promise / Valuable Lesson" • "Wakko's 2-Note Song / Panama Canal / Hello Nurse / The Ballad of Magellan / The Return of the Great Wakkorotti / The Big Wrap Party Tonight" Season 4: "One Flew Over the Cuckoo Clock" • "Cutie and the Beast / Boo Happens / Noel" • "Jokahontas / Boids on the Hood / Mighty Wakko at the Bat" • "A Very Very Very Very Special Show / Night of the Living Buttons / Soda Jerk" • "From Burbank with Love / Anchors A-Warners / When You're Traveling from Nantucket" • "Papers for Pappa / Amazing Gladiators / Pinky and the Ralph" • "Ten Short Films About Wakko Warner / No Time for Love / The Boo Network" • "Pitter Patter of Little Feet / Mindy in Wonderland / Ralph's Wedding" Season 5: "Back in Style / Bones in the Body" • "It / Dot - The Macadamia Nut / Bully for Skippy" • "Cute First (Ask Questions Later) / Acquaintances / Here Comes Attila / Boo Wonder" • "Hooray for North Hollywood" • "The Carpool / The Sunshine Squirrels" • "The Christmas Tree / Punchline (Part I) / Prom Night / Punchline (Part II)" • "Magic Time / The Brain's Apprentice" • "Birds on a Wire / The Scoring Session / The Animaniacs Suite"