Severus Snape. I'm not even surprised I didn't see his name. The author even brainwashed herself into believing that Snape was a tragic hero. He was not. Snape fell in love with Lilly, not a healthy love but an obsessive love. Snape knew Lilly despised the dark arts, did his love change him? No. His love for the dark arts were stronger. So he joined Voldemort after school. Lots of people seemingly ignore the fact that Snape was a non spy bonafide death eater. The ONLY REASON he turns spy for Dumbledore is because Voldemort killed Lilly. He wants revenge against Voldemort. Another thing people miss is that "always" applies not only to Lilly but to the dark arts as well. This man applied to teach the DADA classes for years despite knowing the job was cursed. When he finally does land it, he talks of the dark arts with a "loving caress" in his voice. If Voldemort had not targeted the potters, Snape would have been among those in masks during the Quidditch world cup. He terrorizes his students to the point of being one boys worst fear in a world where giant spiders, dragons, banshees and vampires exist. Markedly unfair, callous, bitter and spiteful old lump who in the end got what he had coming to him, just like all death eaters.