It's pretty simple: Batman's nickname is The Dark Knight, the same way Superman's is The Man of Steel. The title came pretty quickly in Batman's development: Detective Comics #45 in November of 1940: about a year and a half after his first appearance ever. Basically it's a clever way of saying "This is a Batman movie!" without actually putting "Batman" in the title.

And it's a pretty apt description of who he is. He's a knight because he's the good guy of course: standing watch over Gotham City and protecting its people from any threats, no matter how freakishly dressed or ridiculously evil. But he doesn't do all that in the daylight, oh no. He slinks around in the shadows, employing questionable methods and generally scaring the peewuttons out of any criminal he runs across. Hence, he's a dark one.

Commissioner Gordon sums it all up nicely for us in the last lines of the film: the one mediating on the nature of good and evil and whether or not this protector of the city has actually won anything or not at the end. (We talk more about that down in our "Themes" section.) Any movie that can give us its meaning in two short little words has earned itself a title. And if it sounds as cool and butt-kicking as The Dark Knight, how could it be called anything else?