The Potions Master at Hogwarts and a member of the Order of the Phoenix. Harry has a difficult time believing that Snape is truly loyal to Dumbledore, given that he was once a Death Eater, continues to follow Voldemort as part of his work for the Order, and hates Harry and everyone Harry loves with a passion. Snape is a nasty teacher; he plays favorites and torments the students he doesn't like, like Harry and Neville. Neville simply performs poorly under the pressure, while Harry fails many of his assignments because Snape purposefully breaks Harry's vials of potion or Vanishes Harry's potion when he makes a mistake. After Harry's dream of attacking Mr. Weasley as Voldemort's snake, Dumbledore insists that Snape teach Harry Occlumency, a branch of magic that protects a person's mind from attack. These lessons, however—in which Snape tries again and again to break into Harry's mind, with success—are perfect vehicles for Snape to continue to torment Harry, insult him, and make Harry trust him even less. One evening, when Snape is called away, Harry chooses to enter into Snape's memories in the Pensieve to see the memories that Snape doesn't want Harry to find. Harry discovers a memory that shows him how his father James and Sirius taunted and tortured Snape for no reason as students at Hogwarts. Following this, Snape refuses to teach Harry Occlumency. Like several of the other professors, Snape understands the necessity of seeming to support Umbridge, at least superficially. This is why, when Harry asks Snape for help in code in front of Umbridge, Snape pretends to not understand. He does, however, alert Dumbledore and the rest of the Order, who are then able to save Harry and his friends from Voldemort at the Ministry.