Severus Snape is a fictional character in J. K. Rowling's Harry Potter series. He is characterised as a person of great complexity, whose coldly sarcastic and controlled exterior conceals deep emotions and anguish. In the first novel of the series, Snape is a teacher who is hostile from the start toward Harry. As the series progresses, Snape's character becomes more layered and enigmatic. Rowling does not fully reveal the details of his true loyalties until the end of the final book, Harry Potter and the Deathly Hallows. Over the course of the series, Snape's portrayal evolves from that of a malicious and partisan teacher to that of a pivotal character of considerable intricacy and moral ambiguity.