Horace Slughorn is a fictional character from the Harry Potter Universe.
Horace Slughorn was a former Potions Master in Hogwarts before his first appearence in Harry Potter and the Half Blood Prince. He was at Hogwarts when Tom Riddle was still in school. He was in his "Slug Club" along with Riddle's soon to be Death Eaters.
Slughorn first appeared in the Harry Potter and the Half Blood Prince. When Dumbledore came to Privet Drive to collect Harry, he had to stop in on Slughorn because he wanted him to teach again. He pretended to be attacked when they came to the house that he was in, and Dumbledore quickly found him hiding as a couch. He left to go to the bathroom, and left Harry with Slughorn. Harry convinced Slughorn (though unintentinally), to resume his post. Harry thought he was going to be the DADA teacher, but when they returned to school, they saw he was the Potions teacher, and Snape received the DADA. But while on the train before the feast, Harry and Neville got invitations to join Slughorn for lunch in his compartment. When thet got there, they saw two seventh years, a boy named Zabini, whom was a Slytherin, and Ginny. He explained who everyone was and how everyone was connected. He said Ginny cast a great Bat-Bogey Hex on another student.