Joker Didn’t Kill Anyone at Bruce’s Fundraiser for a Reason
This theory from Redditor poeir (perhaps more an observation than a fully fledged theory) suggests that Joker crashes Bruce Wayne's fundraiser in The Dark Knight to confirm his belief that Harvey Dent is Batman. He wasn't there to kill anyone, but to unveil Batman's identity. The evidence? Well, firstly, Joker states, “For a minute there, I thought you were Harvey Dent" at one point. Later in the film, Joker toys with Dent when he’s shooting at his convoy; it seems like he's not even really trying to kill him.
Here’s the theory, in all its glory. If you haven't seen The Dark Knight in a while, it might be a little confusing:
"First, when the Joker arrived at Bruce's fundraiser for Harvey Dent, the Joker wasn't randomly killing people--he had a plan, and part of what made his plans horrifying was his ability to tell the police exactly who he was going to kill and then kill them. Killing random bystanders doesn't accomplish that. When the Batman (who the Joker thinks is Harvey Dent) jumps out the window to rescue Rachel, the Joker expects them to be the same person, so there's no reason to keep looking for Harvey Dent at the party.
Later, when Harvey Dent is being transported by police, the Joker uses an escalating series of weapons against the convoy, but doesn't use the rocket launcher on the paddywagon containing Harvey Dent. The only weapons he uses are ones that can't penetrate the paddywagon's armor, and he gradually escalates to make the threat to Harvey Dent seem real. He does this to discover if they really are the same person: If the Batman shows up, Harvey Dent isn't Batman. If the Batman doesn't arrive, Harvey Dent is Batman.The Joker never wanted to kill Batman (he says as much in the interrogation scene, 'I don't, I don't want to kill you! What would I do without you? Go back to ripping off mob dealers? No, no, NO! No. You... you... complete me.'), he wanted to force Batman to break his 'one rule.' A dead Batman cannot be corrupted, so as long as Harvey Dent might be Batman, Dent must not be killed."
Robin Is a Potential Weapon Against Batman
As comments on this theory point out, the idea that Robin is a safeguard against Batman seems like a genuine plot from a cartoon or comic, one it would be interesting to see in the future. The theory posits that Bruce Wayne himself put Robin in place just in case Batman loses it and becomes a villain.
The theory, from Redditor acidityregulator, states:"What Batman fears more than anything is turning evil. He is perfectly aware he is capable of doing so, and just about no-one would be able to stop him if he was a villain. But what if there was a person who knew his fighting style and weaponry inside out and back to front? What if there was another person with his skill and similar life experiences, yet far more young and optimistic than Batman?"
The Joker Is a War Veteran
Redditor hokky points out that Joker in Christopher Nolan's The Dark Knight is an intelligent tactician and capable fighter. From holding his own head-to-head with Batman to planning his escape from the police station, it's clear he's not some rando civilian. Add on top of that the trauma, PTSD, and insanity that comes with serving time in a war zone, and it seems plausible that the guy who withstands Batman’s brutal interrogation may have been a prisoner of war once upon a time.A commenter on this theory made note of the fact that, during The Dark Knight, when giving examples of his problems with society, Joker says if “…A truck load of soldiers will be blown up, no one panics, because it’s all part of the plan.”
See what else was part of the Joker's plan here.
Batman Is a Patient at Arkham Asylum
Reddit user slugboy questions whether the death of Bruce Wayne’s parents cracked his mind, leading him to create Batman and the entire Gotham universe in his mind. Alfred, unable to take care of an insane young Bruce, sent him to Arkham Asylum. The people Bruce encountered in the asylum became characters in insane Bruce's Batman drama.
As per this theory:"Alfred would come to visit and attempt to be the voice of reason, but never could really get through. Dr. Jonathan Crane tried various methods to snap Bruce back into reality, but Bruce's reality is so terrifying that he receded back into the delusion. Dr. Edward Nigma, a therapist, would try to reason Bruce back in to the real world, but Bruce would twist his words into riddles. So, he continues to chase these villains and bring them to Arkham Asylum from which they will inevitably escape - because they were never actually incarcerated."