Byung-hun Lee did not receive an Oscar nomination for portraying Soo-hyun Kim in I Saw the Devil.
It is always interesting to see how a film will play differently when re-watching it, and the earliest scenes of the film have all the greater impact when you are aware of what is coming soon. Lee in the brief scene where Kim speaks with his fiancee is actually rather devastating with this knowledge in that he does provide a real warmth in the brief scene where Kim attempts to find a moment to romance her while doing his security scenes. It is a genuinely sweet moment where Lee just reveals a normal guy in love, which naturally in this film is not meant to be given that she is murdered as the opening scene of the film. In discovering the murder Lee is moving in portraying the honest grief of Kim as he initially discovers his painful loss. This however changes from the moment he decides to exact revenge by finding the killer. Lee puts that obvious gentle humanity to Kim in his very quiet portrayal of the state of Kim once he begins his descent into hell. Lee's fashions this exact state of Kim as this man filled with vengeance, and is outstanding what he does with his restraint in the role.
Lee shows a man no longer seemingly broken by his loss rather completely in charge of his existence. There is this undeniable power to the presence of Lee as he is frankly more menacing than the killer he assaults. Lee portrays this with the right limited emotions at times of a man who is essentially focusing himself away from his sorrows, and into the path that gives himself purpose. This is not to say it is unemotional in the slightest. Lee is incredible in the way he stays so quiet yet brings such a palatable intensity in his eyes. His eyes that suggest this hatred that fuels the man on his quest. This though again often has this certain calm and in doing so Lee does not make Kim some otherworldly hero simply doing the right thing, for him it's unfortunately far more complex. In that intensity there is this confidence, and seemingly some ease in his being. A contentment most of the time in his drive to get revenge. In the early scenes where he directly faces the other criminals, or Choi's Kyung-chul Lee brings this detachment within the intensity as though he is acting as some spirit of vengeance who is beyond their limits of understanding. Lee's terrific as this technical facade is actually made properly believable, and what makes him so menacing.
That state is always Lee's point of return in his performance and it so effectively reveals the frame of mind of the man who is finding some strange solace in his quest. This is not to say there are not moments of breaking, Lee in fact brings this at the right moment, such as when he finds his wife wedding ring he naturally reveals a bit of the pain again. That though he wisely keeps restrained still keeping Kim as the properly stoic "hero" that you would find in most revenge thrillers. He returns though always back to seeming in a place away with it whenever he is on his quest. This is to the point in his initial confrontation with Kyung-chul Lee stays almost without emotion in the fight, until he has knocked the killer unconscious and is about to be able to kill him. Lee reveals just a bit of his pain seeping in even within the apparent satisfaction as he is about to commit the coup de grace, and in this Lee makes the strange choice to let Kyung-chul live convincing. In that moment Lee suggests the thought of a man about to lose everything falling back into his despair, and makes sense of the man letting the killer live since if he tortures him it gives him something to keep him going and away from his despair.
Lee shows this as allowing Kim to continue his state of that confidence, that power as he follows and pesters the man trying to drive him insane, well...more insane. Lee brings that detachment, that what would usually be described as sort of a cool bad ass detachment, of the man whose going to make life for the villain a living hell. Lee constantly appears with that intensity, and absolute control as Kyung-chul's personal judge dispensing punishment viciously, and without mercy. Again this is not truly without emotion however Lee brings it through that palatable contempt to destroy the man. That intensity is as such through Lee's performance that he allows Kim to seemingly become almost the monster himself as he stalks his prey of the killers, with the piercing eyes of a different kind of killer as he seems to stare into their souls, and his voice in these moments which reinforce this unshakable determination in his uncompromising pointed delivery. The more time we spend with Lee portraying Kim on the moment the less simple it become, as he indeed seems less the hero seeking revenge, and man becoming not far off the man he's seeking revenge against.
As with Byung-hun Lee's work in his other leading collaboration with director Jee-woon Kim A Bittersweet Life, Lee is springing a bit of trap with his performance. In that while he is compelling in portraying this more subdued, and withdrawn performance it is building to something. We have hints of this throughout as there are the moments where just a bit of Kim's pain reveals itself, however Lee always portrays this is as only very subtle momentary lapses such as single tear where the emotion pushes itself just slightly through, until the very end of the film where he sets a final death trap to end it all. When Kim leaves Kyung-chul to fate Lee is ice cold as he walks away without emotion until finally the end comes, and the trap is sprung with Lee's performance. Again Lee has stayed reserved for the rest of the film but he finally lapses in this scene revealing finally the full extent of all the pain from the events of the story, and the hollowness he's left with. Lee gives one of the most heartbreaking depictions of grief that has all the greater impact as he shows this usually guarded man finally losing any sense of control. Lee in the scene just lets it all go in such powerful way in this messy combination of tears, and laughs, not laughs of joy rather of a horrible madness stemming from his damaged state. Byung-hun Lee gives a great performance that while perhaps his impact is not immediately as obvious as Choi's it holds the same importance in providing a real emotional depth within the carnage through his complex realization of what revenge does to a man.