Appearing to be the most evil, deranged, and flat out psychotic killer of all comic book villains, The Joker is the primary antagonist of Batman. He is the complete opposite of Batman, in everything from appearance (Batman tends to be a rather large and muscular man, while The Joker is typically a man of average height or even taller possessing a skinny frame), to ideals. The Joker views murder as sport, and will not hesitate to toy with his food before he eats it, even if said food are the men he has hired to work for him. As intimidating as he is psychotic, he still manages to recruit hordes of henchmen despite his maniacal insanity.
The Joker's physical appearance is a polar opposite of that of Batman. Batman uses dark colors such as gray and black to intimidate criminals, while The Joker relies on bright colors, such as purple, green, and sometimes orange to do his bidding. The Joker also has a melted cliche clown face, the origins of which differ depending on the continuity he is used in. Some incarnations of The Joker see him wearing actual make up (such as in the film "The Dark Knight"), while others show his skin actually having been bleached (as in the 1989 "Batman"). He also traditionally has green hair and red lips, to complete the look of the psycho clown.
His methods are unpredictable and incalculable. He does things according to his own twisted sense of logic, and does not desire money. If there was one thing that he did desire, it would be the power to instill anarchy into Gotham by any means necessary, proving that organization is meaningless and futile. He is an exceptionally intelligent man, and this tends to be his greatest weapon against Batman, the police, and the District Attorney's office. He is often confronted by the authorities, but easily evades capture due to sick and twisted mind games he plays on them, all full of mystery. While Batman prefers to stay in the shadows, The Joker basks in the spotlight, often broadcasting himself to the public and media outlets.
Though he may be Batman's undisputed arch-nemesis, The Joker has always held some kind of respect for Batman, saying in "The Dark Knight", "Why would I kill you? What would I do without you?". He also acknowledges that Batman will never kill him, as that is Batman's only rule, and since The Joker will not kill Batman, they are truly destined to fight forever. As The Joker says, "This is what happens when an unstoppable force meets an immovable object."
Throughout the course of The Joker's involvement in Batman's film and television appearances, he has had many different and diverse interpretations. In the 1960's, Cesar Romero portrayed the character as a campy, funny, strangely psychotic, yet harmless killer. In 1989, Jack Nicholson played The Joker in a somewhat human way and fashionable to the comics, however upped the "killer" aspect of the character, as well as the quick temper. He also possessed bleached skin in the film, and received a Golden Globe nomination for his performance. In the early to mid 1990's, Mark Hamill voiced the character as icy cold and cruel, vastly different from Nicholson's character interpretation.
In 2008, however, The Joker was taken in a direction he had never been taken before. In "The Dark Knight", the late Heath Ledger portrayed The Joker as a completely psychotic and demonic killer, a sort of Nietzschean superman, with no moral attachment towards anybody but sees Batman as true value to himself. Any humor that the character shows is sardonic and cruel. Ledger's Joker was a personification of disregard and chaos. His primary goal seems to be to prove that people, in dire situations, are just as sick and horrible as he is. This Joker's most frightening and dangerous asset is his intelligence. Ledger was honored with a posthumous an Academy Award, a BAFTA and a Golden Globe Award for his performance.
In all his shapes and forms, The Joker remains as one of the scariest and most ingenious of all comic book villain history.
One of his proudest achievements was turning the well-respected psychiatrist Dr. Harleen Quinzel into his criminal sidekick and 'girlfriend' Harley Quinn. She is madly in love with him; whether or not he returns her feelings is a constant discussion of debate among fans.