In J.K. Rowling’s fantasy novel Harry Potter and the Half-Blood Prince, Horace Slughorn teaches Potions at Hogwarts.
Slughorn returns to the school after being persuaded by Albus Dumbledore. He had previously taught Potions and had retired while hiding from the headmaster. Dumbledore wants Slughorn back partly because he possesses an important memory concerning Tom Riddle, the student who later becomes Lord Voldemort.
When Slughorn resumes teaching, Harry receives an old Potions textbook containing handwritten notes by the mysterious “Half-Blood Prince.” The notes help Harry excel in class, although some of the book’s instructions are dangerous. Slughorn also becomes connected to the school’s wider history because he taught Riddle during Riddle’s time at Hogwarts.
A common confusion is associating Slughorn with Defence Against the Dark Arts, a post held by another teacher in the same novel. Slughorn’s subject is Potions, the class he taught before and after his retirement.