Hermione Jean Granger is a fictional character in J. K. Rowling's Harry Potter series. She first appears in Harry Potter and the Philosopher's Stone, as a new student on her way to Hogwarts. After Harry and Ron save her from a mountain troll in the girls' restroom, she becomes best friends with them and often uses her quick wit, deft recall, and encyclopaedic knowledge to lend aid in dire situations.