Severus Snape taught potions at Hogwarts for for a number of years. He always wanted to teach about Defense Against the dark Arts. He was born on January 9th, 1960. His Patronus is a doe along with Lily Potter, Harry's mother, because its how he professed his love for her. They were always best friends. Snape's doe Patronus professed his one true motivation throughout Harry's life: to protect the child of the women he loved.