As pointed out by The Rowling library: “Fun fact from the Harry Potter TV series: Paul Whitehouse is the first confirmed actor to appear in both the Harry Potter films and the upcoming HBO TV series. While it was announced today that he will play Argus Filch in the show, he previously portrayed Sir Cadogan in the film The Prisoner of Azkaban.”
Sir Cadogan was a wizard and Knight of the Round Table whose portrait Whitehouse played in a Harry Potter and the Prisoner of Azkaban deleted scene. The character’s painting temporarily guards the entrance to the Gryffindor Common Room after Sirius Black slashed the Fat Lady’s portrait.