If there is one character other than perhaps Rick that the show needs to nail, it’s Negan, and that is definitely comparable to the Joker.
Considering there has been chatter and speculation from Walking Dead comic fans about Negan since the very beginning of the series, Norman Reedus definitely has a point that the show’s version needs to be exceptionally horrifying.
Sure, Bruce Wayne is the star of any Batman franchise, but a hero is only as awesome as his villain is awful.
Besides, it sounds like the differences between Negan and Rick are more or less going to stem from how they reacted to the end of civilization, similarly to how the Joker has opined that he and Batman’s differences go back to how they dealt with their “one bad day.”