As Batman: Arkham Knight draws closer, I have been theorizing on the identity of the Arkham Knight himself. My thought came straight after I watched the Ace Chemicals Infiltration trailer below.
Notice, the voice on the radio speaking to the Arkham Knight (who I presume is Scarecrow) tells him that his "....vengeance will come...". This got me thinking, who wants vengeance on Batman that is a brand new character? Then it hit me.....
The Joker's Son
Now, I know you may be thinking "Oh, yeah right!" but hear me out.
In Batman: Arkham City, there is an Easter Egg of a pregnancy test in Joker and Harley Quinn's hideout. The test reads positive which indicates that HQ and Joker are expecting a child.
In the Arkham Knight pictures we've seen of Harley, she is not pregnant as seen below...
Now, how could a baby be strong or old enough to think that it can take on Batman? This is where the speculation comes in. As we know, the Arkham Knight is in alliance with Scarecrow which makes me think that he is the reason that the Arkham Knight could be so much older in this game.
In Arkham City, after fighting Ra's al Ghul while falling from wonder tower, if you go back to the place where Ra's' body is, it will be gone.
I believe that Scarecrow took Ra's' body and used his blood to create a formula to reverse the effects of Lazarus Pit to make the Joker's son older instead of younger which the Pit is well known for. The Arkham Knight now blames Batman for his father's death (Joker's death) and this is what he wants his vengeance for.
Only when Batman: Arkham Knight comes out will we be sure who the true identity of the Arkham Knight is.