With Batman Arkham Knight game by Rocksteady releasing soon we still haven't figured out who the Arkham Knight is, he wears an armoured suit compared to Batman and hides his voice unlike the caped crusader he uses guns and weapons and also fighting skills not batarangs and or gadgets. There is only 7 people who I think might be the Arkham Knight.
1. Jason Todd/Robin/Red Hood
Despite being trained by the caped crusader himself Jason Todd got murdered by Joker until Ra's Al-Ghul took him to the Lazarus Pit and bring him back from the dead he went insane and threatened to kill The Joker as revenge and also stop Batman from getting in his way calling himself the Red Hood who is not only master at hand to hand combat but also master of guns and weapons.
2. Dick Grayson/Nightwing
It wouldn't be a coincidence Nightwing is on this list considering Nightwing was also trained by Batman and being the first Robin until he decided to go solo after Oracle's fake death (or something like that) and maybe he had his mind being controlled by someone or manipulated by Red Hood or Joker telling him that Batman is the enemy also he knows every skill of Batman he knows his weakness so it wasn't a coincidence he's on this list.
3. Ra's Al-Ghul
Ra's Al-Ghul was the one who trained Batman and he is Batman's mentor so he knows every moves Batman will make and counter it Ra's Al-Ghul trained Batman but that doesn't make him a good guy he is also against Batman he's cheated on death many times so why wouldn't he be the Arkham Knight?.
4. The Joker
Joker has a genius level of intellect he is an expert on chemistry and science great hand to hand combat skills and he is Batman's long time rival his long time enemy so Joker must be the Arkham Knight but I'm not saying he's the actual Arkham Knight its just a speculation and besides he's not smart enough to pull that off.
5. Amanda Waller
There was an article before saying that Amanda Waller is our Arkham but you can't judge a book by its cover even a girl can be the Arkham Knight with her skills and weapons expertise she could be the Arkham Knight.