I Saw the Devil (Korean: 악마를 보았다) is a 2010 South Korean action-thriller film directed by Kim Jee-woon and written by Park Hoon-jung. Starring Lee Byung-hun and Choi Min-sik, the film follows NIS agent Kim Soo-hyun (Lee), who embarks on a quest for revenge when his wife is brutally murdered by the psychopathic serial killer Jang Kyung-chul (Choi).