14: Cory Monteith.
Image Source: alchetron.com
Known by Gleeks around the world for playing Finn, Cory Monteith was a talented actor and teen heartthrob. He was recording for TV shows, starred in a couple of films, and was just maturing into the sort of actor he had always dreamed of being, when he died. He was found in his hotel room, having combined alcohol and illegal drugs, resulting in an accidental overdose.