The founder of the Slug Club returned from retirement to teach at Hogwarts at Dumbledore's request. Slughorn formerly taught Potions to Harry's mother Lily, and Tom Riddle, the latter of whom convinced Slughorn to disclose information on becoming immortal. Later, Riddle murdered Harry's parents. Ridden with guilt on aiding Riddle, Slughorn modified his own memory, but Harry was able to convince him to disclose the truth with the help of a good luck potion, Felix Felicis.