Kane!
Kane is my absolute favorite character of the series!
I love how at first I thought he would be the typical villain of the show, but then it turns out he's not a villain or a hero - he is a human being, trying to do the best he can, and sometimes he fails and makes mistakes.
I love that sometimes you wanna hate him, and sometimes you just love him. He is truly complicated like all humans are, but the shows doesn't try to show him as a hero like Clarke, or a villain like Murphy was in the start.
And of course, it doesnt hurt that he is portrayed by they very good looking Henry Ian Cusick ;)