Deathstroke already appeared in Batman: Arkham Origins (and was arguably the best thing in it!), but Rocksteady does not consider that game canon. We have yet to see their version of the character. Already wearing a similar looking suit of armor and equipped with a whole plethora of weapons, the Arkham Knight is basically just Deathstroke with a Batman mask. With so many villains already having fallen to the Caped Crusader in both games, it is reasonable to assume that they would want to avoid facing him again, and hire someone else instead. Who better to hire than the worlds greatest assassin? Slade Wilson has always been a fan favorite, but he has only recently seen a resurgence in popularity after appearing in video games Arkham Origins and Injustice: Gods Among Us. Then there was Manu Bennett's charismatic and terrifying portrayal of the character on Arrow, and Warner Bros recent announcement of a Suicide Squad movie that could potentially see Deathstroke finally debut on the big screen. We don't know if Slade Wilson will be revealed as the Arkham Knight, but Rocksteady will miss out on a serious opportunity if he isn't included in some capacity.