Arrow has cast its Season 4 villain with Neal McDonough playing Damien Darhk.
Via DC:
As teased last season on Arrow, Oliver Queen and his team of allies will have a new adversary to deal with—Damien Darhk. Described as a mysterious and sophisticated villain, and an adversary of the late Ra’s Al Ghul, Damien Darhk is now the leader of his own clandestine group, suggesting that this cunning foe will prove to be one of the Arrow’s greatest challenges.
Neal McDonough is known for Band Of Brothers, Justified, Captain America, Minority Report and voiced Deadshot in the animated movie Batman: Assault on Arkham.