John Williams

It certainly helps that his music is closely associated with the most successful and one of the best mainstream Hollywood filmmakers ever in Steven Spielberg, and that he's also done scores for other films--Star Wars, Superman--that were among the biggest/most successful in cinema history. Star Wars may be THE biggest film franchise ever, and it's a film score that everyone who hasn't been living under a rock knows. I think John Williams, much like Spielberg, is pretty much the best at what he does. The question has always been about the value of what's being done, rarely about the skill with which it's done.