L Lawliet from Death Note.
L Lawliet. Pretty much my favourite enigma. We know very little about him, and this is oddly for the better. All we really know is that he's from Winchester, England, and holds a relation to an orphanage called Wammy's House. We also know that he is freakishly intelligent, thinks like a computer, and really, really likes sweets.
It's odd how a character that, in terms of plot, could have been replaced by a supercomputer or something, manages to endear himself to the audience. It's not for nothing that he has an army of fangirls, to a degree that I often forget how much I loved Death Note just because of the godawful fandom. L is, in a word, an eccentric. He is loaded with as many quirks that make him not only fascinating to watch, but also very fun at the same time. His unique way of sitting, his odd mannerisms, his use of percentages in speech (which, according to the author, is a load of bullshit that L made up), his dry, monotone voice... it all adds up to something very unusual, and very loveable.
It is a shame that we never really come to see any character depth in L, though it could have ruined the mystery of him if it had been added. That said, the expansions onto the Death Note verse (such as BB Murder Cases, the Death Note extra chapters, and L Change The World) are gradually adding small bits and pieces, like L's morality on criminal cases... or rather, deliberate lack of.
L: "Please turn off all cell phones, laptop computers and any other transmission equipment and leave them on the table over there."
Matsuda: "I know he's being cautious from the start, but does he really trust us or not?"
L: "No, I just hate it when cell phones ring when I'm talking."