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Baek San is the main villain of IRIS and Iris 2 is NST director and head of IRIS is reposbile for death of Kim Hyun-jun's parents and father to Jung Yoo-gun who was main character of IRIS 2
Yoo Sang-joon was a respected Nst Agent who worked with Wi Sang-chul during his mission he met Jung Soo-min in 1978 they dated for many years until Soo-min become pregnant with their child, Sang-jun deiced to quit his job and buys flowers to her when Sang-jun received call from Soo-Min was hold hostage by his group caused him to saved his love before he was beaten and unconscious
At Tokyo Sang-jun woke up when Sang-chul told that Soo-min was killed along with their child but to unknown to him that Soo-min was still alive and gave to birth a son - Jung Yoo Gun who become main character of sequel of the series. Sang-jun was renamed as Baek San during his days he was recruited by Antony Choi who is owner of IRIS as assassin, His targets include parents of Kim Hyun-jun who left him as witness when Baek San shot and killed his parents. he would adopted Anothey's daughter Seung-hee as daughter
Baek San met Kim Hyun Jun at office
After three years since the events, Baek San still impriosned in the cage and IRIS tried freed him
he met his son Yoo Gun for first time is now is member of NST although he never knew his son