Of all the characters in the Harry Potter universe, Severus Snape may be the most intriguing. He starts off as a cruel professor, one who makes the Boy Who Lived's time at Hogwarts miserable from the start. He then murders Albus Dumbledore, in a twist that left fans reeling. But, by the end, it was revealed he was a good guy and a character with immeasurable depth and intrigue, so much so he probably deserves a standalone book (one day).