The Joker is Nyarlathotep
Lawrence Gowan's "A Criminal Mind" is about the Joker.Think about it:
Joker's actions toward Harley in Death Of The Family were his attempt at getting back at herThink about it: he's dead for like 5 minutes and she f*cks Deadshot. Even a sociopath like Joker would be hurt. He felt like she replaced him. So he tries to give her a taste of her own medicine. But his twisted mind means he takes that Up to Eleven: telling her he never loved her and throwing her in with a bunch of dead bodies that he claimed were past Harley Quinns (he lied) to make her feel just as replaceable as he felt. Really, the whole arc can be summed up as Joker seeing how well everyone had adjusted to life without him, and feeling a little offended by it.
Joker is the Bat Spirit of Arkham Asylum.Apparently all of Jokers origins center around Batman and considering how Joker is clearly feigning insanity to avoid the Death Penalty and that he commits crimes out of a desire for fame and notoriety it's likely that he was the one who terrorized Amadeus Arkham and his mother into insanity. When Batman showed up and was treated as the supernatural Bat Spirit the Bat "Spirit" became furious and sought to become an enemy of Batman to reclaim notoriety and fame thus becoming Red Hood. After falling into chemicals and becoming the Joker the Bat "Spirit" saw a way to reclaim notoriety and fame while tying the legend he started to Batman who would in turn be tied to him.
In relation to the "Joker is the Bat Spirit of Arkham Asylum" WMG Joker became the Joker deliberately.The story of Jack Napier checks out except for one thing: There was a third leader of the group who Napier was betrayed to... What's more Joker showed fear over Batman knowing his true identity despite telling Batman the Jack Napier story. Therefore Joker wasen't Napier but the third leader of the group or should we say the real leader of the group... It's so convienient that the Bat of Arkham/Red Hood fell into a pool that turned him into a clown(basically the opposite of a bat). The Bat of Arkham experimented on chemicals until he got the formula to create permanent clowns(so that he couldn't be unmasked) than used the most usable factory chemical worker(namely Jack Napier) to create a vat of chemicals that would turn him into an clown. When the guy's job was done the Bat of Arkham would arrange for him to "have that one bad day" than kill him and dispose of the body when it was over in order to give himself a easily verifiable backstory and then don the Red Hood and lead his men into the factory where Batman would almost certainly show up and beat him leading to the Bat of Arkham Asylum falling into the vat and becoming the Joker.
Joker plans to have Batman kill him in order to restore the Bat of Arkham Asylum's reputationAs shown in the comics the Joker survived a bullet to the head so if Batman deals a fatal blow to the Joker it wouldn't be fatal yet would give Joker a means to fake his death then reappear in Wayne Manor in the form of the Bat of Arkham Asylum to kill Bruce Wayne. The reason the Bat of Arkham Asylum dosen't do that earlier is to publicly prove to Gotham that Batman is the Bat of Arkham Asylum and not an imposter cribbing off his style. If Batman kills someone the world will think he was the Bat of Arkham Asylum all along and just faking goodness. If Batman dies as an old man then Joker will be forced to face the publicity of having the Bat of Arkham Asylum's reputation ruined. What kind of reaction he would have from this is unknown.
Joker is Trigon the Terrible's father and thus Raven's grandfather.Trigon is called the halfbreed son of one of a mystic cult's gods and a female of said cult yet they don't mention that god's name.... At one point in time Joker became Emperor Joker with Myxlplyx's powers which believe it or not include Time Travel which could easily help Emperor Joker become Trigon's divine father and be the source of Trigon's demonic nature.