Baek San (36 episodes, 2009-2013)
Oh Hyeon-Kyu / Oh Hyun Kyu (31 episodes, 2009-2013)
Park Cheol-yeong / Self (26 episodes, 2009-2013)
President Jo Myeong-Ho / Jo Myeong-Ho (25 episodes, 2009-2013)
Kim Seon-hwa / Self (21 episodes, 2009-2013)
Kim Hyun-Jun / Kim Hyun-jun / Self (21 episodes, 2009)
Choi Seung-Hee / Choi Seung Hee / Self (21 episodes, 2009)
Jin Sa-Woo / Jin Sa Woo / Self (21 episodes, 2009)
Jung Yoo-Gun (20 episodes, 2013)
Yoo Joong-Won (20 episodes, 2013)
Ji Soo-Yeon (20 episodes, 2013)
Kim Yeon-hwa (20 episodes, 2013)
Seo Hyun-Woo (20 episodes, 2013)
Nightclub Owner (20 episodes, 2013)
Young Jeong Soo-min (20 episodes, 2013)
Park Sang-Hyeon / Park Sang Hyun (19 episodes, 2009)
Hwang Tae-Sung (19 episodes, 2009)
Deputy Director Choi Min (18 episodes, 2013)
Ray / IRIS soldier (17 episodes, 2009-2013)
Yang Mi-Jeong / Yang Mi Jung (17 episodes, 2009)
Yang Jung-In (17 episodes, 2009)
Joong-Kwon / Park Joong Kwon (17 episodes, 2009)
Kang Byung-Jin (17 episodes, 2013)
Kang Cheol-Hwan / Director Kang Cheol-Hwan (17 episodes, 2013)
Yoo Hae Young (17 episodes, 2013)
Yoon Shi-Hyuk (16 episodes, 2013)
Hong Soo-Jin (16 episodes, 2009)
Jung Hyung-Joon / Jung Hyung Joon (16 episodes, 2009)
Kim Ji Hun (16 episodes, 2013)
Pyo Jin Hwan (15 episodes, 2013)
Vick (14 episodes, 2009)
Yoo Kang-Oh / Yoo Kang Oh / Vice Director Yoo Kang-Oh (12 episodes, 2009)
Park Tae-Hee (12 episodes, 2013)
Song Yeong-Min (11 episodes, 2013)
Park Choon Sung (11 episodes, 2013)
Yoo Jin (10 episodes, 2013)
Jamie (9 episodes, 2013)
Rie / Erica Sato (8 episodes, 2009-2013)
Young Ki Eun (8 episodes, 2009)
Lee Cheol-Min (8 episodes, 2013)
Lee Soo-Jin (8 episodes, 2013)
President Ha Seung-Jin (7 episodes, 2013)
Jung Soo-Min / Yoo-Gun's Mother (7 episodes, 2013)
Chief of Staff / Chief of Staff Goo Gong Gil (6 episodes, 2013)
Young Baek San / young Baek San (6 episodes, 2013)
Lee Hyuk-Soo (6 episodes, 2013)
Yoo Jung-hoon / Mr. Black (5 episodes, 2009-2013)
Hwang Soo (5 episodes, 2009)
Yuki (4 episodes, 2009)
Ha Jae-Yong (4 episodes, 2013)
Oh Hyeon-Kyu's Nephew (4 episodes, 2013)
IRIS soldier (3 episodes, 2009)
Kim Hyun-Jun (child) (3 episodes, 2009)
Young Ji Soo-Yeon (3 episodes, 2013)
Park Joon-Han (3 episodes, 2013)
Young Jung Yoo-Gun (3 episodes, 2013)
young Jung Soo-Min (3 episodes, 2013)
North Korean Agent (2 episodes, 2009-2013)
Kang Cheol-Hwan (2 episodes, 2009)
Yoon Sung Chul (2 episodes, 2009)
Chinese Firearms Dealer (2 episodes, 2013)
John (2 episodes, 2013)
Captain Jung (1 episode, 2009)
Self (1 episode, 2009)
Shin Yoo Sub (1 episode, 2009)
Oh Hyun Kyu (1 episode, 2009)
Takashi Yamamoto (1 episode, 2009)
Japanese IRIS Soldier (1 episode, 2009)
Phillip (1 episode, 2013)
Jang Chul (1 episode, 2013)