Lee Chum Foon was a notoriously melancholy and phlegmatic character, but was he that way by nature, or did he become that way due to his experiences (particularly with Lam See Yam and Lung Siu Wan)? My impression is that even in his salad days, Lee was a naturally melancholy individual, and his experiences with Lam and Lung compounded the melancholy that had always been there.
Underneath all that melancholy, though, Lee also had this sarcastic sense of humor that suggested a mischievousness that belied the grim persona.