Joker

His birth name unknown, little is known to anyone about the Joker before he became what he is, save for his being the product of man's failure.

A genius in many regards, the Joker was accidentally permanently disfigured to have white skin, green eyes, and a red rictus grin. Taking his appearance to heart, he became a clown-themed Super-Criminal, utterly unpredictable in his crimes, ranging from highly complex terrorist plots with a high kill count to simple, seemingly harmless gags, so long as they make him laugh.

Seeing Batman as his equal and opposite, The Joker's seeming motive in life, beyond creating mayhem and suffering, is to convince Batman of his radical philosophy.

When Batman tries to see the inherit good in man, Joker only sees the bad. When Batman works to the bone to keep saving Gotham, Joker chaotically encourages entropy. When Batman lives by a strict code, Joker lives by no rules.

The Joker believes that because man is capable of evil, man is inherently evil, and that even "good" people are evil at the end of the day, thus making "good" people not worth saving.

In Batman, Joker sees someone aware of this philosophy but who refuses to accept it. Seeing Batman's positive influence is in direct contradiction to the Joker's belief system, so he'll do anything he can to make Batman see his way and abandon his cause.

No act, murder, torture, rape, and no victim, men, women, children, is off limits to the Joker because by the nature of his belief he views them as being just as bad as he is, and just another pawn necessary to convince Batman to his belief.

Initially trying to prove his point to Batman by convincing children to commit atrocities, when Batman refused to claim his victory by killing him, the Joker made it his quest to force Batman to kill him and thus make Batman confirm his philosophy.

Along the way, Joker had devised several plans to present a challenge to Batman, some making sense and others having no apparent reasoning.

In order to truly get underneath Batman's skin, the Joker killed his sidekick, Robin, tortured Jim Gordon, and crippled Barbara Gordon.

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Early Life
Jack Napier, the engineer and comedian; Jack Napier, the mob boss; The Dissident Rambo Drifter; Arthur Fleck

Origin
"You're late."

The Red Hood approached the mobsters just outside Ace Chemical Plant. "Where were you, ya clown?" the thinner of the two mobsters asked. "We have a precise window. Once that window closes, you lose your head." No response from the hooded figure.

"Careful man," the fatter mobster interrupted. "That could be the boss for all you know. If the other guy didn't show."

"Yeah right. Does that look at all like the boss to you? And wouldn't he, you know, be talking?"

"Maybe he jus' wants to preserve his identity for the tapes."

"Whateva. Let's go, rookie."

The man beneath the dome nodded and the three men began moving to a break in the chain link fence.

Each man squatted down and crouched into the grounds. The helmet was heavy and blinding on the man who wore it, tinting his every sight blood red. They walked among the vats, making their way to the ladder to the catwalk. From the catwalk, they could enter the foreman's office; from the foreman's office, the basement; from the basement, the old boarded up tunnel to Monarch Playing Cards.

regarding the break in the fence-- the mobsters had already scoped that much out. They still needed Jack so as to have a reliable guide through the factory. Sure, they studied floor plans, but they had never experienced it.

Napier meets Napier (picked because he had the same name)

First, Jack gets some second thoughts, when approached by the mob boss of the same name and his goons (remember, they could have bribed anyone in the factory; they chose Jack because they found out he had the same name when searching for marks, and he just so happened to be desperate. The boss tells him that if he backs out, he'll see to it that his wife is killed, and he'll do the job himself if he must. From there, as security, and since they don't care about things like humanity or decency, they do have his wife killed in a fire by crooked cop Oliver Hammet, and, inadvertently for the mobsters, Jack is informed when he is eating with the mobsters and telling them he still feels nervous. Despite his objections they still strong arm him. Whether or not he puts on the red helmet and becomes the Joker is ambiguous. However, Riddler still witnessed it. Unlike in the comics, where for some inane reason Joker tells Riddler and Riddler spontaneously is aware of Joker's identity, there is a rare moment of Riddler trumping Batman-- but only because of happenstance. Because he lived near Jack and had seen his face and had seen Jeanie die, it was only a little bit of digging for him to have a solid hunch that they could be the same person. Even then, though I am of the opinion that Jack is Joker, here he does not give Riddler a definitive answer, but decides to protect him for the kicks. From Batman's perspective, there are many different men who could be the Joker, some of whom are drifters with no names, and he is frequently preoccupied. He never had the info that it would even be an inside man. Perhaps in the time of Beyond he can Detective vision reconstruct the scene and solve it.

The First Laugh
The "buffer" story between The First Laugh and the Man Who Laughs is Riddler's more proper debut. Fitting for the character, after already being sidelined during the Dark Moon Rising, he only gets a shorter story here. He relays his riddles through a blimp, which of course he claims is his work, but in actuality is the work of Professor Flakey. This inspired the GCPD to turn to Flakey and use him to make patrol blimps as they get more clean, or perhaps more extreme, and the Joker eventually commissions one that ends up in an exanded Scooby-Doo crossover with Penguin too. This is also the time that Hugo Strange, now fascinated with the Batman, is appointed to profile the Batman while the task force is formed. The trite bit about Catwoman is here too (also from Prey,) and the city is still trying to figure out what the hell to do in light of the Joker's plot. After his second attack, Strange and the other doctors propose their solution in Arkham Asylum, and more of the story regarding Scarecrow from Terror makes its way into Harvest of Fear.

The Man Who Laughs
Furious from his defeat by Batman, Joker crafted a second, less calculated, but even more deadly plan. When before he seeked to send a message to Batman and Gotham, now he would show how dangerous he was by killing them all by poisoning the water. This when Batman finds out that Joker was once the Red Hood, and he played a hand in his creation.

There's a brief period between these two Joker stories, rather than setting this  one after Harvest of Fear, for a number of reasons. One, the immediacy of Joker's turnaround is important. It shows that he's angry and been offended, and that he has a dangerous temper. Two, having him wait too long in Arkham would not cause him particularly to stew. He'd come up with a better plan with that much time. It must be a reaction, not a response. Three, his having blown up some stuff and almost more truly held the city by the throat, but not in a way that every citizen felt, like forcing Batman to blow up the dam would, which would then give ample reason for the Arkhamites to come in and propose their solution. Four, these two stories in this order would experience no change in how they make Joker a threat to Batman and Gotham, but having Scarecrow torment Batman with psychological warfare is a strong wrap up to his inaugural year that makes him realize he truly can't do this alone. Fifth, it gives room to expand a little on characters who appeared in that previous story, such as Firefly, who maybe even worked to help the Joker, who knows, and give Catwoman a little breathing time to be a crook before getting even more tied up with Batman.

Harvest of Fear
After the series of horrific events in Gotham correlated with the supervillain boom, including Joker's own child-bombing plot, Jeremiah Arkham and a team of other renowned doctors set to reopen the since decayed and defunct Arkham Asylum as a means to house and treat the super criminals. With major funding and security provisions from Wayne Enterprises, the asylum was rebuilt both to function as a prison and a hospital. Along with the likes of Firefly and Solomon Grundy, Joker would be included in the inagural class of inmate-patients-- what would be a bright hope for rehabilitation would be dashed by their sickening evil.

During the time Joker was incarcerated, Doctor Hugo Strange (who was tasked with the Joker's treatment) and Doctor Jonathan Crane (as the Scarecrow) both found themselves in conflict with the Batman.

Joker's Asylum
A combination of Batman: Arkham Asylum, Arkham Asylum: Living Hell, and Arkham Asylum: A Serious House on Serious Earth, with traces of what the Arkhamverse was before City, such as the full Rogues gallery, and antecedents of the Arkham storyline. Featuring Joker, Harley, Ivy, Scarecrow, Bane, Croc, Clayface, Great White Shark, Hugo Strange, as well as several more minor villains from both the silver age and Living Hell. If Joker's dressed more "seriously," he doesn't take his philosophy of the world being a joke as seriously. Joker's creation of his monster army can come from Hugo's Monster Men, (notes he'd gleaned in his time in Arkham over the years) Venom, and Penelope Young. Maybe this all causes Hugo and Sharp's demises (but not necessarily deaths), thus allowing the new blood in Arkham, as Hugo's research is discovered and his experiments on patients can finally be proven. There is an adjacency to some extent to the actual Arkham continuity, so, how does the Joker overcome the terminality of the compound? Does Batman save him? The Arkham City plot has already been foiled. UTRH takes place not long after; Arkham City would have given Jason a few years to really build up a force but those plans are discovered by Batman and of course circumvented.

A Clockwork Indigo
Batman contemplates the morality of giving Joker an Indigo Lantern Corps ring to make him compassionate. However, he ultimately decides it is worse to chance a man's nature and can't go through with it or tries to undo it. But it won't be so easy...

But ultimately he returns to his evil ways

The Dark Knight Strikes Again
Though The Joker was gone, his impact had lingered. Jason Todd, in spite of all of his fighting, would break and take the Joker's identity to oppose the returned heroes of the past, specifically Batman.