This is Horace Slughorn. He is played by Jim Broadbent inn films 6, 7pt1, and 7pt2. HE can turn into an armchair. Thats what he was disguised as when Harry saw him for the first time. In Harry's 6ht year he was the Potions teacher and Snape took place as the Defense Against the Dark Arts teacher. When Riddle was still in Hogwarts he was Slughorn's favorite teacher. He told Riddle what a Horcrux is and how to make one. At first Harry and Dumbledore when into the memory of Slughorn but that one was meddled with. So after trying forever Harry finally got the real memory and found out the truth.