You either die a hero, or live long enough to see yourself become the villain.
Now I'm fairly certain I've been saying that line for at least ten years, don't know where I heard it, but now someone pointed out I was referencing The Dark Knight and I honestly couldn't believe it when I googled the phrase and found nothing but Dark Knight sites.
It's highly likely that the quote originated from The Dark Knight movie. Apparently, Batman (and other super-heroes) was inspired by Friedrich Nietzsche, a German philosopher. A lot of aspects of Batman are inspired by Nietzsche's beliefs which would explain why the movies seem very philosophical at times.
Along with the fact that there seem to be no references to this quote prior to the movie release (or any variation of it), I conclude that it did in fact originate (at least main stream) from the movie.
This quote does originally come from the film. Harvey coins the phrase (no pun intended) in response to Rachel's comment abot Caesar. He isn't using a common expression, but it does come off quite eloquently. Still it is very similar to the philosophy of Michael Foucault who criticized political and social figures who turn to abusing power for indulgent convenience.
I agree that it's almost difficult to believe, but sometimes Hollywood coins a phrase that really resonates.
Another example of a phrase that everyone uses but which came from a modern day movie: "bucket list" from the film The Bucket List (2007). Nobody had ever used that phrase before the film was produced.