Horace Slughorn, Harry Potter and the Half-Blood Prince. Professor Slughorn shows off a love potion on the students’ first day of class—reminding them that there’s a caveat. 24.

Credit: Warner Bros. If HBO truly intends to modernize Harry Potter for a new generation, it can’t afford to treat love potions as a joke. In the books, Voldemort’s mother, Merope Gaunt ...