Joo Won as Gaksital / Gangto / Sato Hiroshi.
This drama is no doubt one of the best k-drama I have ever seen. Watching it constantly put me on the edge of my seat since it is very emotionally draining and the roller-coaster ride that drama gave me is simply unforgettable. Until today, I have yet to find a drama that could give me that kind of excitement again. ;_;