High Quality Content by WIKIPEDIA articles! Robert Arthur "Rob" Knox (21 August 1989 – 24 May 2008) was an English actor who portrayed Marcus Belby in the film Harry Potter and the Half-Blood Prince, and had signed to appear in the planned film Harry Potter and the Deathly Hallows. He died after being stabbed outside a bar in Sidcup, England, in May 2008, when he intervened in a fight to protect his brother.