Who is Arkham Knight? Honestly, I was a little disappointed in the design. He reminded me of the generic "Evil Version of Hero" trope. However, my opinion changed in a few moments, and it has grown on me (he still looks like Batman+Ironman, not that thats a bad thing!). He could give the Arkham-verse Batman a run for his money. So the real question is, who's under the helmet?
1. Hush
Hush, real name Dr Thomas Elliot, was referenced to in Arkham Asylum and made his debut at the end of Arkham City, revealing that he has given himself.cosmetic surgery to look like Bruce Wayne. A few days ago, the Arkham FaceBook page teased an announcement for Hush (which I thought was going to be more DLC for AC). Then we get the announcement of this game. In the comics, Hush and Riddler organize all the villains in an attempt to finally stop Batman. This seems like the synopsis given for AK. While Hush wasnt a hand to hand combatant, the Arkham Knight Hush very well can be.
2. Joker
In one way, I'd be really disappointed if it's Joker AGAIN. In another way, how could they leave out the center of the series? But, I'd really prefer it to be someone other than Mr Jay, as him being alive would undo a great ending of AC. Also, in an interview about AK, Sefton Hill says the Joker is "dead dead dead."
3. Jason Todd
I'd love it to be Jason, but, and correct me if I'm wrong, we havent had any reference to Jason in the series. So I'm not sure if he'd fit in. However, Batman's "greatest failure" would be a great villain for the finale. The Arkham Knight's suit also resembles Todd's in "Battle for the Cowl".
4. Damian Wayne
With the title of the trailer being "Fathers and Sons" this is a high possibility. He is a highly trained assassin, grandson of Ra's al Ghul. I've always imagined Arkham-verse Batman as mid to late 30s, so a teenage son is possible.
5. Thomas Wayne
Going with the "Fathers and Sons" theme, this is an unlikely but worth mentioning possibility. How he would become a villain is up to them, but he could have training like in Flashpoint, and want vengence on the city that failed.
6. Original Character
I wouldn't mind a bad ass original character to give Batman hell.
Honorable Mentions: Thomas Wayne Jr, Ra's al Ghul, Azreal, Bane