The CW has cast Neal McDonough as the previously unseen villain Damien Darhk in Arrow Season 4.
Though he hasn’t yet been seen on screen, Darhk did play a role in Arrow Season 3, described by Ra’s Al Ghul as an ally turned enemy.
The Arrow producer describe Darhk as “a mysterious and sophisticated villain, and an adversary of the late Ra’s Al Ghul. Now the leader of his own clandestine group, this cunning foe will prove to be one of the Arrow’s greatest challenges.”