Unfortunately, many of the excellent actors in Harry Potter are no longer with us. They have passed away since filming the movies. Some of those people include Alan Rickman, Richard Griffiths, Richard Harris, and Roger Lloyd Pack. Arguably the most tragic death of all was 18-year-old Rob Knox, who played Marcus Belby in Harry Potter and the Half-Blood Prince. He was stabbed in London after rescuing his brother from a man who was threatening him. There was even a documentary made about it, entitled (K)nox: The Rob Knox Story.