Galatea Merrythought

Professor Galatea Merrythought was a former Hogwarts Defence Against the Dark Arts teacher, mentioned in Harry Potter and the Half-Blood Prince. She retired during Professor Slughorn's previous term as Potions Master, in Tom Riddle's last year as a student. Riddle's ambitions to succeed her in this position were thwarted first by Armando Dippet, and later by Dumbledore. After this, Riddle supposedly cursed the DADA job, meaning that no DADA teacher is able to teach in this position for more than one school year. Merrythought was employed by Hogwarts for more than fifty years. Her name implies that she was adept at conjuring the Patronus Charm.