The Joker is a homicidal maniac and the archenemy of Batman. Although his real name and full origin are unknown, the Joker is known to have been forced to swim through a vat of chemicals which turned his skin white, his hair green, and left his face permanently locked in a double Glasgow Grin. Completely unpredictable with no regard for human life, the Joker finds murder and mayhem funny, and is perhaps the most dangerous man on New Earth with a body count stretching into the thousands, all centered around his obsession with destroying the Dark Knight.
Accounts of the Joker's origins have been varied and numerous. He himself has told the story of how he came to be with several different variations, saying that sometimes he remembers it one way, sometimes another; and that if he has to have a past, he "[prefers] it to be multiple choice." What has remained the most consistent is that his first encounter with the Batman was while he was acting in the identity of the "Red Hood," along with a gang of other thugs, committing a robbery in or near the Ace Chemical Processing Plant. During this robbery he either tripped into a vat of chemicals, or was accidentally pushed in by Batman.
Most origins end with him falling into chemicals which bleach his skin, make his hair green, and give him a permanent red smile. Sometimes the chemicals are also blamed for his mental state, and the combination of chemical exposures, and possible brain damage due to oxygen deprivation have been cited as factors in his insanity.
The various versions of Joker's origin invariably include Batman's involvement in some way, and whatever the reason he fell into the vat of chemicals, he blames Batman. During a lucid state the Joker admitted "Here's the cold, hard truth Bats...I don't hate you 'cause I'm crazy...I'm crazy 'cause I hate you."
His activity between the accident in the chemical factory and his first public appearance as The Joker is unknown, but his return to the Gotham City crime scene was a spectacular one. He announced himself on television, after murdering a reporter with Joker Venom, and publicly told the police he intended to murder local millionaire Henry Claridge that evening on the stroke of midnight. Despite a full compliment of GCPD officers guarding his apartment, and intervention by the Batman himself, Claridge collapsed to the ground at midnight in a fit of laughter and died with the Joker's trademark death-grin on his face. The Joker also nearly contaminated Gotham City's entire water supply with his poison, but Batman was able to stop him by cutting off the reservoir's connection himself; effectively forcing the entire city into a drought as a consequence. The Joker was successfully incarcerated, but not for long.
Gotham City Life
Incarceration would prove no obstacle for the Mirthful Menace, and he quickly rose to become one of the top members of Batman's Rogues Gallery. He would find a frequent home in Arkham Asylum, Gotham's local insane asylum, where he would most commonly find himself imprisoned. Despite the asylum's efforts to contain him, he viewed it as sort of a revolving door, and even a place to simply rest up between his plans. His crimes vary from the whimsically indifferent to the inhumanly brutal, and his plans, in Batman's own words, "make sense to him alone." Many henchmen are afraid to work for him, and he doesn't always necessarily intend to physically gain from his crimes. He often commits crime for the sheer enjoyment of it, or specifically to cause pain to others, which he sees as part of "the big joke." Although not all of his criminal endeavors earn him money, he has been shown to have a significant bank roll, and has had possessions as outrageous as a full truck-mounted heat-seeking warhead.
The Joker has a substantial list of significant crimes, so many that his entire criminal history is too lengthy to be recounted. His most consistent theme has been personal attacks against Batman, often through loved ones and members of the Batman Family, but he has shown complete indifference as to who his victims are, as it doesn't really matter to him. Though many fear to form an alliance with the Joker, the Clown Prince of Crime was recruited into a gang of super-villains led by Two-Face to battle Carmine Falcone's criminal empire. As one of the Joker's tasks, the Joker had to eliminate Mario Falcone, but the hit was unsuccessful. The group was also responsible for the Columbus Day Massacre of Gotham's mob bosses, including Bobby "The Don" Gazzo. The team disbanded after a battle with The Hangman and the battle in the Batcave with the newly-formed Dynamic Duo, Batman and Robin.
While the Joker's criminal activities have certainly not been limited to those listed here, he has performed a considerable number of acts that distinguish him from the population of ordinary villains.
The Killing Joke
While trying to show Batman how easy it was for even the sanest of people to lose their minds, the Joker attempted to drive Commissioner Gordon insane. He arrived at Gordon's house, and before kidnapping him, shot his niece in the spine then took pictures of her naked, bleeding, and in pain on the floor, and forced the Commissioner to watch in a slideshow. Although the Joker did not know this when he shot her, James Gordon's niece was actually Barbara Gordon, a.k.a. the original Batgirl. She was left crippled, a wheelchair-bound paraplegic, and forced to retire from her life of street vigilantism to a new career as the mysterious "Oracle" for a time.
A Death in the Family
In one of his more heinous acts the Joker murdered Jason Todd, the second boy to don the guise of Robin. Jason had been searching for his mother in Africa, and found out too late that she had actually been involved in criminal activity with none other than the Clown Prince of Crime. Jason's mother betrayed him, and the Joker tied the two of them up together in a warehouse set to blow up. He also viciously beat Jason with a crowbar many times, causing severe trauma to his head. Batman was unable to rescue the two of them before the bomb's detonation, and they were both killed in the explosion.
When Bane destroyed the walls of Arkham Asylum, Joker escaped the facility. Before leaving, he left Dr. Arkham in a death trap to stall Batman.
A few days later, Joker teamed up with Cornelius Stirk and used him in a plan to kidnap Commissioner Gordon in order to control the GCPD. His plan was foiled when Stirk tried to kill Gordon instead of kidnap him and Joker left Stirk to be captured by Batman. As soon as he was leaving, Joker was approached by Scarecrow and together they teamed up and invaded the house of Mayor Krol. They dosed him with Scarecrow's Fear Toxin and forced Krol to do their will. Joker was having fun with Krol and after Scarecrow pressed Joker to think of an evil plan, Joker told him to make Krol call the president of the union of firefighters and inform him that he was cutting their rolls. Joker did this, knowing that Firefly was creating fires all around Gotham. Joker then forced Krol to call the GCPD and give them a false instruction to rescue him at a funhouse. Joker prepared a trap that caused the death of the entire SWAT Team of the GCPD.
No Man's Land
During the time Gotham City became known as "No Man's Land" (when it was abandoned by the United States and crime ran rampant across town,) the Joker was absent for quite a while. Batman also left Gotham for some time, and while he was away the Joker just simply didn't think it worth the bother of being active in Gotham. However, when he did appear, amidst the already burgeoning chaos, his impact was shocking. A large number of GCPD officers were murdered when he, after capturing them, dressed them up in costumes and makeup similar to his own, so they would all be killed by a lone police sniper who had a vendetta against the Joker. A large number of innocent police officers were shot by their comrade.
Later, he took an entire hospital ward full of newborn infants hostage. When Detective Sarah Essen, Jim Gordon's wife, arrived on the scene, he pointed a gun at her and told her not to move, but then threw a baby at her. Sarah instinctively went to catch the child, and the Joker shot her in the head. Oddly, he seemed to take no pleasure in this act. When Gordon found out, his anger led him to the verge of murdering the Joker but instead he only shot Joker in the knee. The Joker was immediately concerned about the damage to his leg, worrying that he might never walk again, but quickly cracked up laughing, realizing there was a joke. The Commissioner had just gotten him back for the damage to his niece.
At one point the Joker stole Mister Mxyzptlk's reality-altering power, remaking the entire world into a twisted caricature, with everyone in it stuck in a loop. The Joker entertained himself with various forms of murder, such as killing Lex Luthor over and over, and devouring the entire population of China. Ever obsessed with Batman the Joker tortured and killed his adversary every day, only to bring him back to life and do it over again. Superman's powerful will allowed him to fight off the Joker's influence enough to make contact with the weakened Mxyzptlk, who along with a less-powerful Spectre, encouraged Superman to work out the Joker's weakness before reality was destroyed by the Joker's misuse of Mxyzptlk's power. As time ran out, Superman realized that the Joker still could not erase Batman from existence, as the Joker totally defines himself by his opposition to the Dark Knight; by this logic, the Joker would be incapable of destroying the entire universe, since he is incapable of doing so to Batman. This broke the Joker's control, and Mxyzptlk and the Spectre reconstructed reality from the moment the Joker disrupted everything. However, Batman was left broken from experiencing multiple deaths and Superman had to erase Batman's memories of these events so that he could go on.
Joker's Last Laugh
In an attempt to get him to come to terms with his mortality and have some sort of moral realization, a prison doctor informed the Joker he was going to die of a malignant tumor. Instead, the Joker decided he wanted to leave his mark on the world indelibly, and began a chain of chaotic events that would come to be known as "The Joker's Last Laugh." He used a variant compound of the Joker Venom to actually Jokerize all metahuman inhabitants of Slabside Penitentiary, driving them virtually into the same condition he was in, but with the added benefit of having every single one of them completely loyal to him. The Joker's army ravaged the planet, combating all of earth's heroes, but Batman was eventually able to thwart the attacks using an antidote he obtained from Harley Quinn. Harley was angry at the Joker for attempting to impregnate her without marrying her. Nightwing, falsely believing that Robin had been eaten in the ensuing madness by Killer Croc, caught up with the Joker and actually beat him to death. Batman, not wanting Nightwing to have blood on his hands, resuscitated the Joker and saved his life.
Hush and the Riddler convinced and manipulated several other villains into helping in their attempt to destroy Batman. Part of this included fooling Bruce into believing that his childhood friend Tommy Elliott was the latest victim of the Joker. That brought Batman to the brink of murdering the Joker, and he only stopped when former GCPD commissioner Jim Gordon talked him down, reminding him that by killing the Joker, Batman would become just another killer, and Jim refuses to let the Joker ruin Batman's life in that way.
In "Soft Targets", Joker began a shooting spree with a high powered sniper rifle murdering Mayor Dickerson and the Superintendent, in order to force the inhabitants of Gotham City to stay inside during the Christmas holiday. He then turned himself in to Gotham's Major Crimes unit, before revealing he'd planted bombs throughout the city, as a "Christmas present" for Batman. This caused the M.C.U. to rush to save countless Christmas shoppers from death. Joker then began a shooting spree within the Major Crimes Unit, where he killed several detectives, only to be shot multiple times by Maggie Sawyer, as his bomb went off, leveling a now evacuated toy store. Joker recovered from his wounds in the hospital laughing at the carnage he had caused.
Under the Hood
After Jason Todd returned to life, he sought revenge against Joker. Todd took over the Joker's old Red Hood identity and found Joker on an abandoned carnival, where he beat the Joker with a crowbar in the same way as Joker did to him years ago.
Shortly after this, Joker recovered and learned Black Mask's latest scheme and confronted the crime lord, who was disguised as Batman. The real Batman arrived shortly after and knocked down the Joker before chasing Black Mask. However, during his fight with the crime lord, Joker managed to get away. Some time later, Joker got a second chance to take down Black Mask and he shot the crime lord on the leg. Joker's vendetta against Black Mask was due to the killing of Robin at the hands of Black Mask, as the crime lord was blamed for Stephanie Brown's death. Joker was mad at Black Mask for taking away from him the chance to kill another Robin. Batman arrived at the scene and stopped the fight, delivering both criminals to the police and Joker was sent back to Arkham Asylum.
A few days later, Red Hood abducted the Joker and held him hostage at Crime Alley, beating him without mercy until Batman arrived. Jason tried to force Batman to kill Joker and then he threatened to do it himself. However, Batman defeated Jason and Joker seized the chance to create havoc by taking a gun and shooting a box of explosives, blowing the entire building.
The Joker was one of extremely few villains not drafted into Alexander Luthor's Secret Society of Super-Villains during the Infinite Crisis. Unlike many of the other villains, like Catman, the Joker actually wanted to be a member of the Society, but the higher level members wouldn't let him join, which enraged him. While slaughtering a branch of the Royal Flush Gang on his warpath, the Joker was actually laughed at by the King who said "Don't you get it? The Joker's too Wild!" He then electrocuted him with his joy buzzer, before walking away and saying to himself, "That's not funny". Later, after the Society had been defeated, while Alex Luthor was planning what to do next, he was ambushed by the real Lex Luthor and the Joker. Before allowing his brutal murder, Lex simply told his counterpart "You should've let the Joker play."
For a period the majority of Earth's villains were deported to the Hell Planet, where the Joker became responsible for one of the factions. They were largely nonconstructive, and attempted to steal food and supplies from Lex Luthor's group, who were trying to find a way to escape. The conflict ended in one-on-one fisticuffs between Luthor and the Joker. Although the match was nearly even, the Joker ultimately overcame Lex, just before the entire villain community was forced to unite against an oncoming Parademon attack.
Jimmy Olsen interviewed an incarcerated Joker about the murder of Duela Dent, who had called herself "The Joker's Daughter." The Joker stated that he never had a daughter, but expressed awareness of the Multiverse's existence and of shifts in reality.
The Clown at Midnight
A deranged police officer impersonating Batman, named Josef Muller, shot the Joker in the face, leaving him physically scarred and disabled. After having undergone extensive plastic surgery and physical therapy, The Joker reappeared with a drastic new appearance, with scars running from the corners of his mouth high onto his cheeks, and affliction sometimes referred to as a "Glasgow smile." While in intensive care at Arkham, the Joker had developed a new, more lethal variant of Joker Venom, and instructed Harley Quinn to use it to kill his former henchmen to signal his spiritual "rebirth." He then went on a rampage through Arkham, attempting to murder Harley (her death being the final "punchline" of his rebirth) before being stopped by Batman.
Joker was locked in his cell in Arkham when suddenly Batman showed up and attacked the Scarecrow in front of Joker's cell. Batman opened the cell, cuffed Joker to a pipe and proceeded to torture Crane on the Joker's toiler, much to the madman's delight. After Crane confessed his crime, Batman left the place and Joker was thankful with him for letting him witness such a great performance.
Not long after this, Joker was offered a position on Doctor Hurt's conspiracy "the Black Glove" and he murdered several people on Arkham as part of the plan. It was revealed that Joker joined Black Glove on the condition that they give him Robin and not long after this, Guy Dax freed Joker from his cell. Joker then attacked Dax and mutilated his face after going for his henchmen and after a while, he attacked El Sombrero, apparently killing him. Joker went to Hurt and shortly after he faced Batman, who had been lured to Arkham. During the fight, Joker cut his tongue and caused Batman to have a mental breakdown.
After the Black Glove buried Batman alive, Joker warned them that the Dark Knight would rise again and eliminate them all. Then, Joker hijacked an ambulance and escaped Arkham but was pushed off a bridge by a Batmobile driven by Damian Wayne.
Joker soon resurfaced under the guise of British journalist/detective Oberon Sexton. At the same time however, he operated as the Domino Killer, killing members of the Black Glove one by one. Dick Grayson, the current Batman, figured it all out and confronted Oberon about all the domino killings actually being a set routine of jokes. Oberon removed his mask to reveal the Joker grinning at his old foe, the bullet wound to the head seemingly healed.
After the Joker was arrested once more, he appeared to underestimate the current Robin (Damian Wayne) by trying to win the Boy Wonder's pity. He received a beating with a crowbar (mirroring Jason Todd's murder) from Robin, who he realized is the son of his old foe after noting the resemblance between the child and the original Batman. The officers at GCPD ignored the Joker's pleas for help after they concluded that Robin can handle the villain easily.
However, the Joker's apparent helplessness was yet another ruse. Feigning injuries from Robin's assault, he scratched Robin with a paralyzing toxin painted onto his fingernails, and revealed that he had once again manipulated events toward his own ends and mocked Robin for going so far as to provide his own crowbar (another reference to the murder of Jason Todd). Appropriating Robin's utility belt, the Joker escaped to execute his attack on the Black Glove, unleashing his signature venom on an audience gathered under Professor Pyg (via tainted popcorn) and guiding Batman and his allies to a climactic confrontation. The Joker is seen in an undisclosed location, with Robin bound and gagged, and possessing what appears to be a nuclear weapon. Help arrived in the form of the original Batman (who had just returned from his time odyssey), who aided his successor and his son in their battle against the Black Glove and the Clown Prince of Crime in Wayne Manor and the Batcave. Then, the Joker apparently killed Dr. Hurt by infecting him with Joker Toxin and burying him alive. The second Batman pursued and captured the Joker, while the original Dark Knight, Robin, and Alfred Pennyworth disarmed the Clown Prince of Crime's weapon and defeated the remaining Black Glove members.
The Black Mirror
Eventually the Joker escapes from Arkham again by ingesting a mixture of venom mixed with alcohol to secrete through his pores, making him poisonous to the touch. James Gordon's ex-wife Barbara is attacked with more toxin and Batman hunts the Joker down to an underground lair. They fight with Joker refusing to acknowledge Dick Grayson as a worthy successor to "his" Batman, but in defeat he insists he never touched Gordon's wife. It's revealed that James Gordon, Jr. broke the Joker out of Arkham and attacked his own mother with toxin, using her as a diversion while he kidnapped his sister Oracle.
After Earth 2's Batman sacrificed himself to kill a large number of the New Earth Batman's villains, Joker came up to the Dick Grayson of his world and shot him, paralyzing him in a manner not unlike how he had paralyzed Barbara Gordon. Shortly after, he was executed by Telos by breaking his neck, Telos believing him to be repulsive no matter which universe he came from.