He has played many acting roles such as Lucius Vorenus on Rome , as Dan Vasser on Journeyman , as Poseidon on Percy Jackson & the Olympians : The Lightning Thief , and as Dr. Owen Hunt on Grey 's Anatomy . He is known for his prominent television roles , including his performances as Lucius Vorenus in Rome , as Poseidon in Percy Jackson & the Olympians : The Lightning Thief , and as Dr. Owen Hunt in Grey 's Anatomy .