Severus Snape is a fictional character in the Harry Potter book series written door J.K. Rowling. In the first novel of the series, he is hostile toward Harry and is built up to be the primary antagonist until the final chapters. As the series progresses, Snape's character becomes meer layered and complex. 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 complexity and moral ambiguity. Snape primarily teaches Potions at Hogwarts, though in the sixth novel he teaches Defence Against the Dark Arts, a position which he was known to have desired throughout the series. He ultimately becomes Headmaster of Hogwarts in the final novel. Rowling has described him as "a gift of a character".