Early Life Edit
While very little information regarding the Joker's early life before he turned to a life of crime was confirmed, his true identity remained unsolved for the officials of Gotham City, and despite his capture, no traces could be found on his fingerprints, dental records, and DNA matches against the Gotham City Police Department's databases. The Joker's own testimony gave two conflicting accounts describing past events in his life.
The Joker related two stories on how he developed his facial scars. In the first, he told of an abusive alcoholic father who beat his mother. One day his mother took a kitchen knife to defend herself, but he took the knife and attacked the mother. He then came at the Joker and stuck the blade in his mouth, and gave him a Chelsea Grin.
In the second story the Joker mentioned his wife, who was beautiful but had a gambling problem. When she got into debt, the loan sharks carved her face, and she became very miserable. In an effort to make her smile again, the Joker stuck a razor in his mouth and cut his own face, so he would be like her. She couldn't stand the sight of him and left, leaving the Joker always smiling.
The Dark Knight Edit
One month after Batman made presence known in Gotham City, the Joker began making his presence known by committing armed robbery and double homicide, leaving a joker playing card at the crime scenes (which he supposedly earned his name from, with another being that he wears makeup on his face to scare people). Over the coarse of eight months, he enacted in various heists with his gang while disguised as one of the accomplices. The last of these reported robberies was that of the mafia-owned Gotham National Bank, which a group of his men dressed as clowns (Bozo, Grumpy, Chuckles, Happy, Dopey and an unnamed bus driver) who he ordered to kill each other during the heist. Thus, the only thug left standing was Bozo, who was revealed as the Joker himself to the crippled bank manager before making off with the money in a school bus. Interrupting videoconference mafia bosses Sal Maroni, the Chechen, and Gambol had with their Chinese billionaire money-laundering accountant Mr. Lau, about the remaining laundered funds that he hid from the authorities while fleeing to Hong Kong, the Joker explained that Batman is unhindered by jurisdiction, and offered to get him out of the way by killing him in return for half of the money. While the other mafia bosses decline the offer for a while, Gambol refused it by putting out a bounty on the the Joker's head. Later, pretending to be dead, the Joker killed Gambol by slicing his mouth with a knife the same way his father did to him, taking over his empire.
The next day, after learning that Batman has retrieved Lau, Maroni and the Chechen decided on the Joker's offer while recently-elected district attorney Harvey Dent prosecuted 549 of their men. Filming himself torturing Batman impersonator Brian Douglas in a slaughterhouse, the Joker announced to kill selected people each day unless Batman revealed his identity, stringing Douglas's body up outside Mayor Anthony Garcia's window and releasing the video on TV. Making good on this threat by first poisoning Gotham Police Commissioner Gillian Loeb and blowing up mafia trial Judge Janet Surrillo with a car bomb, he even targeted Dent at a fundraiser held in the DA's honor at the Wayne Enterprises penthouse, but Batman's billionaire identity Bruce Wayne hid Dent and left to suit up while his childhood friend and Dent's assistant district attorney Rachel Dawes was approached for Dent's whereabouts by the maniac, who she tried to drive away with a kick in the groin until Batman appeared to finish the attack. In response, the Joker held Rachel hostage and threw her out of the window, leaving Batman rushing rushing past to save her while the clown made his escape.
Following his murder of two men named Harvey and Dent, which he left a newspaper article with a picture of the mayor circled and labeled as his next threat, the Joker disguised himself and his men as the honor guards at Loeb's memorial service to assassinate him. In the resulting mass hysteria, the Joker and his men got away, leaving one of them, Thomas Schiff, behind when he is shot in the leg. Although Garcia survived, Police Lieutenant James Gordon was apparently killed instead after saving him by pushing him out of the way of the Joker's bullet. When the Joker named Rachel as his next victim through Schiff, Dent attempted to draw him out by falsely identifying himself as Batman, the Joker diverted the DA's police transportation using a burning fire engine, then ambushed the convoy in a semi-truck using a shotgun and bazooka. However, the real Batman showed up in The Tumbler, and saved Dent from the Joker's missiles. Now aware that Dent probably wasn't the Bat after all, the Joker took the wheel of his truck and faced Batman, who flipped the truck and crashed the Bat-Pod in resistance on killing him, leaving the clown's arrest open for Gordon, who had faked his own death and was rewarded the title of Police Commissioner immediately aftewards. Thus, the Joker was successfully jailed at the Major Crimes Unit, which he later turned out to have planned the whole time so that he could retrieve Lau, who was also held there, to gain control of the mafia's funds.
When Dent and Rachel were kidnapped by by the mafia through their inside agents in the Gotham Police Department and put in warehouses containing barrels of oil, the Joker was interrogated by Batman, whom he recognized along with himself as freaks outside society before revealing the two locations of both DAs. However, he turned out to have switched their whereabouts to trick Batman into saving Dent, who is disfigured in the explosion while Dawes is killed in the other. Then, talking Police Detective Gerard Stephens into attacking him and holding him hostage with a piece of broken glass, the Joker escaped captivity with the help of a pre-planted phone-activated bomb sewn into one of the henchmen who was arrested with him, Kilson, and Lau in tow. Meeting with the Chechen at the location of the hidden funds, the Joker killed him and Lau by burning the latter alive with the money and ordering the former to be fed to his rottweilers, taking over their empires. Then, to prevent Wayne Enterprises M&A law accountant Coleman Reese from going public on TV with information on Batman's true identity, he threatened on the phone line to bomb a hospital unless Reese is with in an hour, causing civil disorder against the accountant and the evacuation of all local hospitals. During the panic, the Joker snuck into Gotham General Hospital dressed as a nurse to meet with Dent, who raged over Rachel's death, and convince to seek revenge by embracing anarchy, then blew up the hospital during their departures and escaped with a bus-load of hostages.
As Gordon called for the National Guard to secure the city, the psychopath announced his regime to Gotham through one of the hostages, reporter Mike Engel, and warned the citizens to flee if they don't want to cooperate, placing them in an emergency evacuation by ferries. To escalate the chaos, the Joker had two of the ferries separately containing civilians and convicted criminals rigged with explosives, and gave the passengers of each ferry decision to blow up the other by midnight otherwise he'll blow up both from the Prewitt Building construction site. Batman intervened after saving the hostages (who the Joker dressed as his henchmen to lure Gordon's SWAT team into targeting them) and disarmed the Joker of the detonator to both ferries, capturing him with a rope. Although neither ferry exploded, the Joker revealed how his plan was really gonna work: by driving Dent insane to the extent of capturing Gordon's family so that the city would lose hope once the scarred DAs rampage becomes known. Horrified, Batman left the Joker's arrest to the SWAT team, but not before the clown reminded him that their fight may last forever before he dies.