Innocent Man...he's misleading the lead character and letting her think he cares about her, though he's really after her step-mom who used to be his ex-gf that he took the blame for murder so she wouldn't have to, resulting in him getting expelled from medical school and seeking revenge when he finds out she married a rich old guy after he went to jail for her @.@
Missing You - it's not the lead character, but the second lead hides his identity...it's crucial to the story because he's the guy that everyone is searching for, and intertwines his life with the lead female character when they're kids...you should give it a try if you haven't watched it, it's really interesting - the actual lead character is just trying to get his first love back
Personal Taste - Lee Min Ho's character pretends to be gay so he can live with the female lead