Ask any comic fan, who is the Batman's greatest villain? Pretty much 10 out of 10 times they will say the Joker. Now while I do like the Joker I think from a more intellectual standpoint, Ra's is Batman's best villain. How many times did you watch a episode of Batman The Animated Series and actually think that the Joker will defeat Batman? None exactly. Just the fact that Ra's Al Ghul main goal is to kill 3 billion people to restore earth to its natural form, makes for awesome story lines. Batman's wit and strength is tested to a breaking point every time he fights Ra's Al Ghul. Batman has almost died at the hands of Ra's Al Ghul. You really see Batman's detective skills come to life whenever he has to stop a national eco-terrorist from killing 3 billion people. I also respect him for his purpose. He is tired of seeing earth being reduced to a fog infested world. His methods are crazy but his purpose is honorable. If I had to hire one guy to kill Batman it would be Ra's Al Ghul. Anyways the only villains from the rouges gallery that could really challenge Batman's intellectual prowess is the Riddler and Ra's Al Ghul. Every body else has some major flaw that always prevents them from defeating Batman. In finality to me Ra's Al Ghul is Batman's greatest villain because of his back story and his intellect.