- Well, no masks for me. I have nothing to hide. I laugh at the cruel absurdity of the world. But Batman... Batman, he's got them all fooled. He's made them think he can make a difference. That he can actually make things better. And the joke of it is, they all believe it!
- — The Joker src
The Joker's past is unknown. Conflicting, unconfirmed reports state that he was a failed comedian, a petty thief, and a broken family man. He is an unrepentant homicidal maniac, albeit without a precise psychological diagnosis. His white skin, green hair, and blood-red lips belie the chaotic nature underlying his cartoon appearance. The self-styled Clown Prince of Crime has no superpowers beyond a capacity for incredible violence and a skill at creating deadly mayhem. He frequently concocts elaborate schemes to entrap his arch nemesis Batman.
The Joker, as he tells his origin, began his criminal career as the masked Red Hood. During a heist at a chemical plant, the Red Hood encountered Batman, and during the scuffle, fell into a catch basin. The Red Hood's mask saved his life, but he was left permanently disfigured. When he saw the extent of his disfigurement for the first time, he lost what was left of his sanity and embraced madness.
Determined to give Gotham City a better class of criminal, the Joker targeted Roman Sionis, a wealthy businessman and, secretly, a crime boss calling himself Black Mask. The Joker kidnaps Sionis and assumes the Black Mask identity himself, acquiring funding for more ambitious operations. He places a $50 million bounty on Batman which attracts the attention of 8 deadly assassins: the beastly Killer Croc, master sniper Deadshot, swordsman Deathstroke, ninja master Lady Shiva, explosive expert Firefly, Electrocutioner, poison expert Copperhead, and a masked terrorist known as Bane.
After the real Black Mask is freed, the Joker stops using the disguise, but he retains Sionis' resources, including the Royal Hotel, which becomes his new base of operations. After the Electrocutioner is defeated by Batman, the Joker accuses him of gross incompetence and kills him by throwing him out of the hotel. As the remaining assassins scour the city for Batman, Bane stays behind at the hotel with the Joker, correctly deducting that Batman will come to them. Batman arrives at the hotel just in time to see the Joker detonate a series of remote bombs. Outraged by the Joker's callous disregard for human life, Batman proceeds to attack him, but is stopped by Bane. The confrontation is interrupted by the Gotham Police, who have been hunting Batman. An every man for himself free for all ensues, and the Joker nearly dies when he falls from the hotel, but is saved by Batman and subsequently captured. The Joker wonders why Batman would save him, then realizes that Batman has a no-kill rule.
He is taken to Blackgate Penitentiary's psychiatric wing, where he is interviewed by a young psychiatric intern by the name of Harleen Quinzel. Sensing Quinzel's fascination with him, he proceeds to corrupt her. The Joker eventually escapes his confinement during a massive prison riot, seizing the prison's electric chair as his throne. Batman arrives at the prison to defuse the situation, and when the Dark Knight arrives at the Joker's "throne room," Bane is waiting for him. To ensure that Batman will "break his one rule" and kill an opponent, the Joker has synced the electric chair to a heart monitor worn by Bane. However, Batman defeats Bane without killing him. Joker accuses Batman of cheating and begins indiscriminately firing on everyone in the area, injuring the Warden, before fleeing to the prison chapel. An enraged Batman brutally assaults him, but stops short of delivering a killing blow. The Joker subsequently becomes one of the first inmates at a newly reopened Arkham Asylum.
The Joker and his goons raided Gotham City Hall and took the mayor hostage, tying him up and strapping a bomb to his chest. As the Joker taunted the mayor, he expressed his displeasure that Batman hadn't shown up, who ironically attacked moments later. The Joker tried to escape via a large parachute, but was stopped by Batman, who proceeded to escort the Joker to Arkham Asylum.
Joker takes over Arkham in an elaborate trap set for Batman and spends most of his time watching Batman with the use of the Asylum security cameras, taunting him as he makes his way through the island. His ultimate goal, however, is to combine a more potent plant-venom hybrid called Titan with his army of thugs, which he manipulated the higher-ups into transferring to Arkham in order to create "an army of a thousand Banes".
He then sends the recently released Bane, Poison Ivy, Scarerow, Killer Croc, Zsasz, and Harley Quinn to run interference alongside his thugs against Batman to slow him down. After foiling the other villains' agendas, Batman confronts the Titan-enhanced Joker atop Arkham, which is televised across Arkham by Jack Ryder. Joker is defeated by Batman and once the prison island is secure he is relocated to his cell once again.
Arkham City & Final Joke
Six months following the events of Arkham Asylum, Quincy Sharp has been elected mayor of Gotham. At the same time, a criminal duo named T&T, enhanced with Titan, had been wreaking havoc, weakening Two-Face's criminal organization and crippling the man himself. The duo's crime spree ends with a suicide attack on the new Gotham City Hall - an act of terrorism that prompts the formation of Arkham City. Considering these events, and the motivations behind them, Batman theorizes that both the attacks and the mayor's initiative were orchestrated by someone else.
While preparation continues on Arkham City, Batman breaks into Quincy Sharp's mansion to investigate his plans. Confronted by non-lethal security measures, Batman realizes that he is being tested by Sharp's unseen master, and flees the mansion. At the same time, Joker is revealed to be dying as a result of complications from the Titan drug, with an estimated six months to live. Taking advantage of Joker's weakened state, several Arkham guards try to kidnap and kill him. Hearing rumors of the plot, Harley Quinn takes the place of one of the guards and rescues Joker. Harley and the Joker are thrown from their escape boat when Batman attempts to recapture them. Landing within the borders of the new asylum's construction zone, Joker declares himself and Harley the "mayor and mayoress" of Arkham City.
Disguising himself as career criminal Lester Kurtz, Batman investigates the gangs forming in the city. After passing tests from both villains, Batman signs up with both Joker and Penguin. Penguin sends "Kurtz" and several other criminals to steal guns from TYGER, the mercenary unit guarding the city.
The heist goes awry when the Joker's thugs interrupt, and Batman takes the opportunity to destroy the weapons with a grenade. Despite his failure, Penguin decides to let "Lester Kurtz" live so that he can lead a strike force against the Joker only to have him escape. Batman leaves Arkham City in a disguised Batboat, unaware that he is being watched.
Elsewhere in the city, Joker is trying to prolong his inevitable fate by seeing a string of doctors. The latest doctor explains that Joker has been poisoned by a mutated form of the Titan formula, and presents him with a different form of the Titan toxin.
Joker is, later, involved in a turf war in Arkham City against Penguin and Two-Face, but as a result of the Titan-powered venom, he is slowly dying. Batman comes into contact with him after he attempts to assassinate Catwoman, and Joker injects Batman with a sample of his diseased blood, forcing him to try and find a cure to save not only his own life, but the Joker's as well. Although Joker appears to be recovering, his health is revealed to be nothing but Clayface posing as him. Although Batman finds a cure for the disease, Joker accidentally destroys the last of the cure when he stabs Batman in the shoulder with a knife, causing him to drop the vial of it. Shortly afterward, Joker gives in to his disease and dies, his last words being a laugh at the irony that Batman was actually still willing to save him in the end, despite all the pain and suffering he has caused, but Joker's mistrust caused his own death. Batman carries the Clown Prince of Crime from the city, with Catwoman looking on, his thugs broken and Harley Quinn crying out in anguish, and lays him on the hood of a police car, with Commissioner Gordon wondering what happened. The Joker still had a smile on his face as Batman leaves silently.
About a year after the death of the Joker, Batman is struggling to come to terms with the absence of his nemesis and the uncomfortable feeling that the pair shared a bond deeper than either could admit. Without the Joker's chaotic presence, Gotham's citizens have never felt safer, and crime in the city has dramatically declined. However, this gives Batman's enemies, including Penguin, Two-Face, and Harley Quinn, a chance to unite with the singular goal of killing Batman. Scarecrow threatens the city with a chemical weapon in Gotham, forcing the city's citizens to evacuate and Commissioner Gordon dealing with the criminals who remain in the city. The Joker's death haunts Batman enough to where he sees the Clown Prince of Crime after being exposed to Scarecrow's fear toxin. This is revealed to be an expression of a deeper problem: Batman, once contaminated with Joker's blood, is slowly becoming the Joker, physically and mentally, and so are other people.
Joker is in his mind, planning to take the control of the body of Bruce Wayne and nearly does it in a later encounter with Scarecrow. The Joker is a constant presence to Batman, commenting on events and showing as a hallucination. Eventually Batman mentally fights multiple clones of Joker and kills them, only to make Joker's influence stronger. Later, Scarecrow reveals Batman's real identity to the world and poisoned him again, letting Joker take the control. However, since Joker is controlling a fear-poisoned body, he, too has terrifying hallucinations where he initially wins over all his rivals, but then is forgotten before he's stalked by multiple sculptures of Batman who talk to him. In the end, Batman takes control of his body again, locking the Joker away in a prison in his own mind. The Joker pitifully begs for Batman to not leave him alone, but Batman pushes the cage of will into the sea, silencing the Joker forever.
- Superhuman Strength (Formerly)
- Hand-to-Hand Combat (Basic): Joker has shown the ability to take on a large number of guards by himself using a unique form of fighting.  
- Acting: Joker was able to impersonate Black Mask and take over his gang of mobsters for approximately three days and not even Batman knew until he revealed himself.
- Political Science: Joker once ran for President.
- Joker Teeth: Throughout Arkham Asylum and the train station in Arkham City, Batman encounters annoying gag teeth that rattle an laugh. When Joker is injected with TITAN, the Joker Teeth become strapped with dynamite and explode when near Batman.
- X-Ray Specs: These specs allow Joker to see his enemies the same way Batman does when he goes into Detective Mode.
- In one of his P.A. system announcements, the Joker pages for "Dr. Howard, Dr. Fine, Dr. Howard" - the last names of the Three Stooges, which in The New Batman Adventures he has villainous henchmen modeled after, named Moe, Lar, and Cur.
- The Joker's taunt to Aaron Cash, "tick tock, tick tock, is that a crocodile I hear?" - in reference to the appearance of Killer Croc - also references the crocodile in Peter Pan that swallowed a clock and continually haunted Captain Hook with his appearance.
- If Robin plays on the Arkham City challenge map "Joker's Funhouse", Joker will make the comment, "What? Didn't I kill you already? No?" This is a reference to the Robin he did kill, Jason Todd.
- Joker is also known as the Clown Prince of Crime, Mr. J, Puddin', and Masked Hood.
- It is unknown how Joker has survived the fall in the helicopter in "Batman: Assault on Arkham"
- Joker is playable via DLC in Arkham Asylum (only for PS3 consoles), Arkham Origins in the multiplayer mode and in Arkham Knight near to the end in a first person shoot-to-all sequence.
- 41 Appearances of Joker (Arkhamverse)
- 14 Images featuring Joker (Arkhamverse)
- 5 Quotations by or about Joker (Arkhamverse)
- Character Gallery: Joker (Arkhamverse)