I think it's mostly just the hair. Otherwise they don't strike me as too similar.
You know, Doc is always super suspicious of King Radical, but I bet he's not even trying to do anything sinister right now. He's probably going to use his time portal to skip ahead and not have to wait in line, or something incredibly mundane like that. Then Doc will screw it up by being all not-so-stealthy-spy-guy and have to choke out Herschel, which will make the mundane utility be less mundane, and possibly very dangerous. And of course to Doc, this will just "confirm" his ongoing suspicions of King Radical doing something nefarious, even when it wasn't the King's fault.
Long winded theory, but I'm calling it now. Everyone else, place your bets!
"I will not succumb to temptation, unless she's cute."