I want to pick the whole cast of Reply 1997 but I will narrow it down to Sung Siwan's father. He is played by the famous Ahjussi Character actor Sung Dong Il who plays him perfectly every single step of the way.
Siwan's Dad is this poignant mix of gruff, angry, loving, impatient, sweet, awkward man. It does not matter what country you live in or culture you are familiar with... He is an "Every-Dad" You can relate to him. I found myself watching his character and thinking so many times... OH My Gosh...my Dad was so much like him! ...and I grew up in Missouri, USA, on the other side of the world.
Sung Dong Il stole every single scene he was in and made this drama more special for me. He was awesome.