It is unknown who his voice actor is.
It is not mentioned what kind of crimes Thug Neanderthal committed before his final arrest, but they were "especially cruel and senseless". It may be that Darkwing caught him, because he knows who he is.
In jail, Thug signed up for the Adopt-a-Con program to get a chance at early freedom and was taken in by the Muddlefoots. The family's sunny disposition got through to him and he amended his ways, becoming a law-abiding citizen.
Thug Neanderthal wasn't much of a talker during his days of illegal activities, opting instead for grunting and gorwling to appear more intimidating. After spending some time with the Muddlefoots, he loosened up and lost his tough guy act. Taking a cue or two from the Muddlefoots, he even became quite talkative, but with their trademark presumption of the audience's volition.
Thug is a muscular and tall dog with a broad face and brown hair. He used to go for plain, simple clothes, but adopted Herb Muddlefoot's fashion sense after living with him for a few days.
The Muddlefoots participate in the Adopt-a-Con program and are the family to which Thug gets assigned. Unlikely as it once seemed, they manage to reach and reform him. As part of the program's condition that the criminal has to learn a new trade, Herb even teaches him the basics of being a Quackerware salesman, which Thug embraces as his new career.