Outside of pointing at guys like Jason Todd or Hush and assuming they fit the mantle of Batman's new arch-nemesis pretty well, fans have begun speculating far wider possibilities, one of which being the idea that the mostly forgotten-about GCPD (Gotham City Police Department) have long since grown tired of the Dark Knight's vigilante-antics, and have developed the Knight as an advanced A.I. to take him down. There have plenty of run-ins and encounters between the police and Batman himself, with tons of opportunities to study every facet of Bruce's movement and escapist techniques, the programming of which into a full-body system would allow the Arkham Knight to match Bruce blow-for-blow. Rocksteady continue to not yield when it comes to elaborating on the nature of the Knight him/itself, but after taking one look at the extremely futuristic-looking helmet and armour that adorns the new character, this seems like a pretty cool way of creating someone/thing that can match up to the Bat.