The Joker is a Nietzschean who lives in a immoral and chaotic and complicated world. The Joker is all about himself and his monstrous rebellion. He is very self-absorbed and very arrogant, and narcissistic. Although at times in the movie he does have the right to say he is quick, witty, and good at starting mayhem.
The Joker deeply believes in confronting the systems, namely the social, ethics, and morality systems. He feels that these systems only amount to nothing more than artificiality that only weak people operate under. He exists to expose the joke of our pseudo-systematic world.
Thus, the Joker’s goal is to kill, seek, and destroy the superficial ways of this world. Sound familar? The Joker is essentially an anarchist trying to expose that being civil, righteous, and moral is a joke.
The Joker: See, I’m a man of simple tastes. I like gunpowder…and dynamite…and gasoline! Do you know what all of these things have in common? They’re cheap!
Continuously, throughout the movie the Joker creates anarchy to reveal the evil that is just below the surface in our ordinary lives.
The Joker also is manipulative and forceful. He makes people make impossible choices where they either become barbarians like himself or face defeat or death. He is usually (but not quite always) proven right.
Eventually and ultimately good overcomes evil.
So the ultimate question that is underlying in this film is: Do we live in an anarchistic, immoral, dog-eat-dog world, or do we live in a world where goodness exists and ultimately triumphs?
Unfortunately the ultimate joke is on the Joker. suggests that the ultimate joke is on the Joker. The Joker is showing truth, but he is using evil to show it. Batman is for the ultimate good, which means he uses the ultimate good to make Gotham just.
Lastly, it looks like the Joker has some father wounds.
The Joker: [looks directly at Dinner Guest] You know, you remind of my father.
[takes a knife to dinner guest’s neck] The Joker: … I hated my father!