Horace Slughorn is the long time friend of Albus Dumbledore and former Potions Master of Hogwarts. Upon the return of Voldemort, Dumbledore protects his old friend by convincing him to return to teaching (with the help of Harry Potter himself). Slughorn tends to gravitate to students with some form of talent or celebrity. His celebrity encircled society is thus dubbed The Slug Club. As Harry is both talented and famous, not to mention the son of one of Slughorn's favorite students, Slughorn takes Harry under his wing. Seeing Harry does not have a book for potions class Slughorn tells him to go the cupboard to retrieve one. Harry discovers a mysterious book marked 'Property of the Half Blood Prince', which is pivotal in the sixth installment in the series. Horace Slughorn tends to be festive and comical, but he also has a dark side (he was in the Slytherin house), which is revealed when both Harry and the young Tom Riddle/Voldemort attempt to get information about 'horcruxes' out of him. He helps Harry to get that memory, showing he really misses Lily Evans and hates what Lord Voldemort did with her.After Dumbledore's death, he becomes Slytherin's House Headmaster and in the last book, he chooses the side of Hogwarts, showing his ties is with the school, nor with Voldemort. Kingsley Shacklebolt, Minerva McGonagall and him fight Voldemort during the battle and after the end of the war, he presumably stays at Hogwarts.