I have a very unhealthy fondness for Humbert Humbert. Quintessentially he is a figure of deepest sickness and should incite disgust from any functioning member of society, but I cannot bring myself to dislike him, and I think I have worked out why.
Humbert is one of the rare examples of a meta-character* I have ever come across in literature. In almost every situation, a character will be deeply absorbed in his world, battling as he must, experiencing impossible joy, living out the brilliant human experience. But few function as a person does. So often the aim of a character design is to appear real, realistic, tangible. Many come close in morality, irrationality, and passion — but few come close in terms of thought.
A person regularly invests themselves in things outside the events of their immediate life. Art, literature, music, film, every school of thought it given deep concern. I study myself as an entity beyond my own thoughts. I am aware of my faults and my shortcomings, and yet so few characters are. Humbert lays out before his jury, and the reader, every nuance of his mind, every passion, every urge, and analyses himself. That is the key of Humbert — he sees himself, as very few characters can.
Another notable example is Hamlet, who does this on a much smaller scale. Driven by the maddening force of other emotions, his analysis is much less calm, although obvious in his soliloquies. Both Humbert and Hamlet act, observe themselves, analyse their actions and then adapt that information into new thoughts. That is true character development — human development — and it’s what makes characters like Humbert Humbert so powerful.