Muttski is Sonic the Hedgehog's pet dog and loyal companion. After Dr. Ivo Robotnik had launched a successful coup and began consolidating his power, Muttski and Sir Charles Hedgehog were captured and Roboticized during Charles' time running a Chili Dog Stand. Muttski remained an emotionless automaton until his liberation following Robotnik's death at Sonic's hands, and later Deroboticized by the Bem, coming to live with Sonic and Uncle Chuck, as well as Jules and Bernie, in Knothole. Muttski's bond with Sonic strengthened following his return from space, where, courtesy of the alien implant Sonic had installed to be able to translate alien languages, Muttski's normal inaudible woofs were translated into proper speech, allowing Sonic to communicate with him and understand responses. Muttski now resides in New Mobotropolis following the destruction of Knothole. (StH: #43, #50, #123, #134, #175)

Muttski appeared once in his robotic state in the pilot episode of the series of SatAM.

When Muttski "speaks" he is shown to speak in third-person like: "Muttski is happy to have you home again." instead of "I'm happy to have you home again."