Snape is the Potions master at Hogwarts in the series. He is also known to be a Death Eater but after Voldemort started hunting James Potter and Lily J. Potter, the woman Snape had loved since he was a child, he asked Albus Dumbledore to find a safe place for the Potters to hide because he knew Voldemort wanted to kill their son, Harry Potter. As Dumbledore was not able to save the Potters, Snape's sorrow was extremely deep, he gained Dumbledore's trust. Snape was loyal to Dumbledore after this event. Snape killed Dumbledore in the sixth book on Dumbledore's request. Voldemort believed Snape killed him because Voldemort had planned Snape to do that. Snape had let it slip in the third book that Remus Lupin was a werewolf. 