Satire

The Joker is in the opinion of many film critics, the character around which the whole action of the film (The Dark Knight) is built up. A terrorist mastermind only interested in creating chaos. A Joker in a card game can represent chaos for the other players, and can be exciting for the player who holds the Joker card. The basic urge or desire that the player wants is to win, and the Joker card helps the player achieve that desire.

The Joker has a simple anti-conventional nihilistic view point of the world and seeks to disrupt order in a world he does not believe in.

The character of The Joker is usually regarded as a "psychopathic, mass murdering, schizophrenic clown with zero empathy", this is a very striking way to describe a character as it isn't something in which can be related to other characters.

A psychopath is someone who displays personality traits that involve more than simply engaging in criminal acts. A psychopath:

(1) can be superficially charming and manipulative. The Joker is that. Imagine him without his clown makeup, imagine him with a handsome face doing and saying what he does in the film. He'd make a compelling—versus repellant—figure
(2) is emotionally callous, without remorse or guilt. The Joker lies freely when it suits him as he gives two different stories for how he came to have his scars, both likely to be untrue. He doesn't feel bad about his deeds—the lives he taken or ruined or destroyed.
(3) has a socially deviant lifestyle. Not only is the Joker a criminal, but he seeks out the excitement of his life of crime. His crimes act as a drug and he needs the regular fixes of the intense stimulation his actions bring. Unfortunately, he seems to develop tolerance to the drug, wanting ever-increasing "doses" and so planning increasingly sadistic and elaborate master plans.

According to the most basic psychoanalytical model, the character, through his acts and way of thinking becomes the correspondent of the 'id'. This term was developed by Sigmund Freud and refers to “the unconscious, that part of the human psyche which is almost non-human”, yet “dark and inaccessible, a primitive chaos, irrational and amoral". The Joker doesn’t play by the usual rules, because he isn’t motivated by self-interest.

Most criminals are motivated by desire to earn greater wealth, or greater power or to execute some form of revenge or there’s some clear motivation which is understandable. In the case of The Joker you can’t necessarily predict what he is going to do because his motivations are not the normal ones. He has an agenda of destruction, considers himself an 'engine of chaos' and is a unique villain because he’s not necessarily after the money, or power or other traditional things. The deadliest of villains are those with whom you cannot bargain with .In the words of Alfred the Butler, “Some men just want to watch the world burn”. 

The image of the clown is not randomly chosen, but refers back to the Freudian unconscious, seen as intrinsically infantile, since it contains the impulses which were repressed in childhood. His father’s image is strong in his case and deeply marked the route of his existence. “My father was… a drinker. And a fiend. And one night he goes off crazier than usual. Comes at me with the knife… “Why so serious?” He sticks the blade in my mouth… “Let’s put a smile on that face! ... I hate my father”. 

 One shot in particular crystallizes everything that is the Joker as he is walking towards the camera, playing (and, really, that’s the only word) with a bomb detonator. Huge explosions are going on behind him as he walks towards us, stiff and happy and hobbling, like a toddler. He’s a child and this is pure 'id'. At the heart of existence isn’t creation, but chaos.

At the opposite end we discover Batman, or as the film title suggests, The Dark Knight. With the help of Lieutenant Jim Gordon and District Attorney Harvey Dent, Batman sets out to fight against the remaining criminal organizations that plague the city streets of Gotham. The partnership proves to be effective, but they soon find themselves prey to a reign of chaos unleashed by the Joker. These elements can be again applied to the psychoanalytical model developed by Freud. Therefore, Batman and Bruce Wayne  represent the force that fights against the villain, which is in this case The Joker.

Despite the opposition between the two characters (the Joker and Batman), there are certain elements that unite them. There are no references to Batman’s childhood, but information from the previous part of the sequel (Batman Begins) reveal that Bruce Wayne’s childhood was also marked by a shocking experience regarding his parents, having witnessed their killing. Both The Joker and Batmans psyche were  modified by t external influences. This idea is suggested in the film by a dialogue between the two characters.

“Batman: Then why do you want to kill me?

The Joker: [giggling] I don’t, I don’t want to kill you! What would I do without you? Go back to ripping off mob dealers? No, no, NO! No. You… you… complete me.

 
Batman: You’re garbage who kills for money.

The Joker: Don’t talk like one of them. You’re not! Even if you’d like to be. To them, you’re just a freak, like me!” 

At a basic level, the eternal fight between two complementary forces, Evil and Good, can be depicted from the story. The ending of the film comes to reinforce the idea that these two will always exist in the universe and one cannot exist without the other. Batman chooses to save The Joker from falling down the building, not just because he is “the conscience” (the ideal that something controls our sense of right and wrong and guilt), but also because he accepts the existence of a rival force.

His unpredictable actions and dialogue reveals his character's personality, displaying his lack of self-awareness, cruelness and villainous actions. As a result, his characters role serves the purpose of providing an ironic twist to the storyline intended to make others question themselves.

For Batman, there was a great curiosity about this Joker because he hadn’t come across with anybody like him before. This is another character like himself who will not compromise whatsoever. They are dark reflection of each other. The both men operate outside of normal social norms, they are both highly talented, highly gifted on what they do. They have a lot in common.

The Joker wants to see that everybody has a price, that nobody is pure, and that even Batman can be bought or can be leveraged in such a way that he will compromise his principles.

"Do I really look like a guy with a plan? You know what I am? I’m a dog chasing cars. I wouldn’t know what to do with one if I caught it! You know, I… I just do things. The mob has plans. The cops have plans. Gordon’s got plans. They’re schemers. Schemers trying to control their little worlds. I’m not a schemer. I try to show the schemers how pathetic their attempts to control things really are… "

Batman lives within certain self-imposed and socially-imposed rules. Because of those rules, Batman becomes predictable…at least to the Joker. Two men with similar talents, but in the Joker's case, his talents are used to create anarchy for his own amusement. 

I sometimes think that the Joker also has a sort of a romantic attachment to Batman. Not at all sexual mind you, but combination of sadomasochism, compulsive behavior, routine, & single-minded obsession. Hatred is love, murder is sex, pain is pleasure, reality is fake, insanity is sane, & worst enemies are biggest fans.

Madness is like gravity all you need is a little push.