Muttley is Dick Dastardly's canine sidekick. He's a mixed-breed dog, and he first appeared in Wacky Races. Dastardly and Muttley were paired together in various later Hanna-Barbera series, including Yogi's Treasure Hunt, as bumbling villains.
Muttley does not really talk; his main examples of speech are his trademark snicker - a wheezing smoker's laugh (usually made at Dick's expense) - and a mushy, sotto voce grumble against an unsympathetic or harsh Dick (usually along the lines of "Sassafrassarassum Rick Rastardly!"). Muttley also hates bad remarks about him as seen when Dastardly calls him dumb or an idiot as he bites his hand or gritted him angrily to make his owner calm him down. And he is also known as mischievous, understanding, thoughtful, treacherous, lovable, empathetic, astute, menacing, upbeat, truthful, testy, loyal, emotional and sneaky.
In Dastardly and Muttley in their Flying Machines, Muttley wears an orange pilot helmet and white goggles along with a matching orange scarf and he was the one who keeps saving Dastardly from falling and he uses his tail to fly like a helicopter for a brief period. He also has several medals on his fur which causes Dastardly to get the medals back from him. Muttley also has his own show called the Magnificent Muttley where Muttley is a protagonist being taunted by Dastardly who serves as a villain.
Don Messick had used Muttley's distinctive laugh for the character of Griswold in an episode of Top Cat as well as for another Hanna-Barbera canine, Precious Pupp, several years earlier. He also repurposed it for Alexandra Cabot's cat, Sebastian, on Josie and the Pussycats in 1970, and for Mumbly on The Tom & Jerry/Grape Ape/Mumbly Show and Laff-a-Lympics. In more recent years, Billy West is currently the voice to Muttley.
- In the Warrior Princess short, Muttley has been transformed into a giant dragon by Dastardly who portrays as a sorcerer as he retains his scarf and helmet from Dastardly and Muttley and their Flying Machines.
- "Talk about an unlikely matchup": A fanfic of It's So Hanna-Barberaesque picturing Muttley and Mumbly as arm-wrestling competitors