UPN experimented with primetime animation during its run, but had little success. Which also describes the majority of their programming that wasn't either from the WWE or was associated with Star Trek (Veronica Mars being a big exception).
Gary & Mike came from writer-producers Fax Bahr & Adam Small, whose resume included co-producing MadTV for Fox and doing some shows for MTV and its sister networks, such as MTV Unplugged. What they came up with would've been a hit on, say, Fox, but because UPN was in fewer homes, and because Friday night wasn't the hip night for TV it was in the past, the series lasted one season.
Claymation master Will Vinton co-produced the series, which enjoyed a rerun stint on Comedy Central before falling off the face of the earth. Vinton, Bahr, & Small took advantage of their network placement, and managed a crossover with MTV's Road Rules, with the added bonus of then-WWE star Chyna as a guest star in what I think is her only animated gig to date.
Here's a sample from the opener:
Harland Williams (Mike) might be better known today for his guest appearance in the Barenaked Ladies' video for "Falling For The First Time" than this. Kurtwood Smith (That 70's Show) kept Gary & Mike busy. but that's all that can be said.