Gong Yoo
Gong Yoo was eventually cast, and the protagonist's name "Ji Dong-cheol" is similar to the actor's birth name, Gong Ji-cheol. To create the right physique for his role, Gong went on a diet for three months to reduce his body fat. He learned the Russian martial art Systema for the film's fight scenes, and performed car chases, rock climbing and skydiving at the Han River without using stuntmen.