The Dark Knight (possible spoilers)

Arthur Schopenhauer was a German philosopher who came out of the Kantian school but ended up carving out his own little niche that was then carved up by Nietzsche. But before that happened, he talked about the Will a lot. The , and the Will as distinguished from Representation.
Schopenhauer is complicated and difficult to explain. Kinda like Batman. He’s like the Dark Knight of early 19th century Berlin philosophers. Like the Batman to Hegel’s Superman. Sort of.
A Batman In Full
Batman doesn’t need explanation (even though I’m going to go to great lengths to do it anyway), because the story of Batman does not aspire to explain a person. He is also not an allegory. What is Batman? Batman is a hero for a civilization that has cast aside external agency as a first principle. He’s a superhero who is his own cause in a world of supervillains who are their own causes, but they’re all vaguely aspects of the same drive.
Batman is an intuitive, but not simple, symbol of an aspect of Will.
Batman doesn’t have to do the things he does — nothing really causes him to do them. He does it “Because he can take it” — because there’s a quality of him that is inherently motivated, that is driven to survival in an extraordinary way and that strives alongside the other projections of Will in the universe. Bruce Wayne didn’t “make” Batman. He is Batman on a deep level not even he truly understands — because sure, there’s the representation of it, the suit, the batarangs, the batmobile — it’s more than adequately represented. There’s the image. But there’s also the Will of it — not the Batman-in-itself, separate from and bossing around Batman and controlling everything he does (Alfred is a servant, not a master), but the guy actually out there in his suit with nothing but his wits, his batterangs, and maybe his Bat shark repellant.

Let’s talk about the difference between Kant and Schopenhauer for a hot second. Kant argued that for each person there was a “thing in itself” that was separate from the universe we could perceive with our senses and that is the ultimate cause of what we think and do. Sort of like a soul, but not really. More like a mind. (I’m boiling this way down, and so forgive me and flame me in the comments if you like) Schopenhauer argued that there was no reason to separate this function — the part of us that makes decisions and adds value to things — from what was already in the universe. That the thing in itself wasn’t distinct, its functions were just an invisible, separate aspect of ourselves. The subjective versus the objective. The will vs. the representation.
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The relationship between Bruce Wayne and Batman is not cause-and-effect. The Will expressed through Batman is present with and in Batman all the time — you just can’t see it; or rather, you see aspects of it through Batman’s actions, but there’s a facet of it that remains mysterious and outside perception.

Way You Wear Your Bat
In Batman Begins, Batman struggles with whether to himself become this special hero guy, or whether to just give it up or live by somebody else’s expectations. He chooses to be this larger-than life hero, this Will-in-symbol, this walking tribute to trying to make things better.
In The Dark Knight, he has to confront a reality where he isn’t the only one like himself — where the world actually has a number of larger-than-life heroes, Will-in-symbols, people who have strong subjective experiences of Will and objective representations that reflect their intentions. The costume that denotes action. And they can’t all survive at the same time.
Still, there’s this sense of Kinship — they recognize similar aspects of Will within one another.
For one, you’ve got the imitation Batmen — the people who dress up like him, try to take the law into their own hands, and get themselves capped. Batman can’t live with these guys; they get in the way of his work and his mission, which is to keep people like that form getting capped. But he can’t stifle them, either, because once they get an idea in their head that they’re more than just a hungry stomach, well, the idea that you can’t stifle that sort of thing is kind of intrinsic to his worldview. It’s his own tactic, and he understands how difficult it is to stop.
For another, you’ve got Harvey Dent — a different vision of a hero that Batman identifies with strongly, a different fragment, but still cut from the same cloth, or so he thinks. Add the fact that he’s schtupping Batman’s main squeeze. That’s got Schopenhauer written all over it (Schopenhauer liked talking about sex and the competition or sex. He thought it was very important — “Nothing less than the composition of the next generation.”).
And finally, and most importantly, you have the Joker — He gets his own section.

The “Agent of Chaos”
It’s really cool when a movie villain lies. Like just lies. About himself, about stuff around him. It’s silly when a movie villain tricks and deceives everyone around him for the movie, and then when he’s got a moment to talk about himself, he’s totally honest and explains everything exactly the way it works.
I love how the Joker in The Dark Knight doesn’t do that. The second time he explains his scars (and the second explanation is totally different from the first one) is one of my favorite moments in the movie.
Which is why I don’t really take the Joker at his word when he says he’s an “agent of chaos.”
As one of my friends said it better than I could - “For an agent of chaos, he’s awfully well-organized.”
I think he’s speaking to an important point — that, as far as guys like Batman are concerned, with their vision of the world, their own representations to build, their own will-to-life to conduct, the Joker is a destroyer. He just comes in and annihilates power structures, institutions, and, perhaps with the most pleasure, the psyches of people who consider themselves to be righteous and in control — people who feel the are successfully projecting their own version of the Will into the world.
He doesn’t do it for power. He doesn’t do it for money. He does it with a couple of cans of gas and a few bullets, and he burns all the cash he wins in return. He doesn’t seem to have desires that yield to satisfaction — He seems as happy when he’s failed as when he’s succeeding.
I really don’t think he’s anybody else’s agent. There’s nobody “causing” the Joker, and no principle, not even chaos, no Ra’s Al Ghul, no thing-in-itself that pushes the Joker to do the things he does.

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And when he sees Batman, he instantly recognizes somebody like himself. “You’re not like the others,” he says. He gleeful exclaims that Batman is “Like me!”
And this is the villain Batman must strive against to prove his heroism and establish an epic for Gotham.

So, through the Will and Representation, through creating a villain along the lines of Schopenhauer and confronting the need to defeat him, we arrive at the philosophy of The Dark Knight:
To distract ourselves from own desire for pleasure by creating artistic objects in our own image, but also to harness our obsessive hungers. To stamp our own impression on ourselves and the world around us because we think it is a good impression (and because it is a proxy for making babies). To compete with evil even as we see ourselves in it, and, sure, living long enough to see ourselves become the villain — but recognizing that, while our own subjective experience of being the hero is not something anyone else can experience or understand, it is still part of our existence inseparable from the perceived consequences of our actions.