Severus Snape

The professor of potions and the enemy of Harry Potter, he is known as a disliked, mean but witty man who is also the Half Blood Prince, a deatheater, a spy for Dumbledore and an Order of the Phoenix member. Snape appears in all the stories, and is disliked by Harry in every one. He threatens Quirrel in the first book when he tries to break into Fluffy's chamber and the secret hideout for the Sorcerer's stone. He tries saving Harry from Quirrel's attacks during Quidditch, kills Dumbledore in Harry Potter and the Half Blood Prince and loses his life in Harry Potter and the Deathly Hallows as he protects his enemy, Harry.