Black Mask is one of Gotham City's most powerful crime-lords. He has an undying hatred of both Batman and Bruce Wayne alike. Dr. Jeremiah Arkham became "Black Mask II" he was being targeted by Red Hood II. AKA Jason Todd
Black Mask can be unlocked in Villain Hunt (see the article dubbed "Villain Hunt Villains on D.S." for more details). Also on PSP when you finish the game his face will be where you make your own characters.