Jasper is commonly portrayed as a rather goofy redneck dog. In the days of the Pizza Time Theatre, he would uncontrollably laugh at almost any joke, much to the major annoyance of Chuck E., who would often shout "Turn off the fruitcake dog!", which would prompt the backstage technicians to supposedly turn off Jasper, which would stop his laughter and calm him down. On rare occasions, though, Jasper would be so depressed that he couldn't "get his laugh going", prompting the others to try and cheer him up. PTT Jasper was also known for becoming infatuated with most of the Guest Stars, often flirting with them, dedicating songs to them during shows, or simply breaking out in bouts of “lovesick bugling” whenever they were around, much to Chuck’s chagrin.
As the years went by, Jasper's personality became calmer and more laid-back, and his wit became much sharper, especially when having conversations with the other members of Munch's Make Believe Band; he gets into disputes with Pasqually over his eccentric ways and jokes, teases Chuck about Helen’s crush on him, and reprimands Munch about his obsession with pizza. Although he can sometimes come off as cynical, Jasper means well and is always friendly to a fault.
Jasper originally appeared at the original Pizza Time Theatre location in 1977. His original name was listed as "Billy Banjo Boggs" on PTT's initial copyright sheets, but it was soon changed to Jasper T. Jowls. In the beginning, Jasper was voiced by Scott Paulin, who portrayed him as a goofy-sounding redneck. He was often shown to annoy the other characters. Beach Bear's animatronic from ShowBiz Pizza Place, was retrofitted into Jasper during Concept Unification in 1990.
- There was one location in Guatemala City that still had the Jasper and Pasqually animatronics using their latex masks, that deteriorated over time. The Jasper animatronic also had a hole in its left hand. The restaurant closed in 2016, and the animatronic was put on display at the new location, where a Pasqually walkaround head was put on his mask. It is unknown if his latex mask remains under the head.
- Jasper's birthday is on August 26th.