Dark Knight theory explains the biggest mystery about Heath Ledger's Joker

Superhero origin stories might be played out, but there's something about a supervillain origin that keeps us coming back for more. One take on that story just won a handful of Oscars, but the Joker in Dark Knight made famous by Heath Ledger remains shrouded in mystery.

In the decade since Dark Knight first released, Batman fans created their own intricate theories about Christopher Nolan's Joker and his backstory, and one particular narrative has come to be widely accepted among the community. However, a bold new reading of the film casts this popular fan theory in a new light.

If you haven't watched The Dark Knight lately, you should – it's leaving Netflix in March along with Nolan's Batman Begins. And unlike the more recent Todd Phillips adaptation, we never learn a whole lot about how Ledger's character became the Joker.

Many fans have argued persuasively that he's a former soldier suffering from PTSD, pointing to his experience handling military-grade weapons. The movie even seems to support this with one key line from an iconic Ledger monologue:

"If, tomorrow, I tell the press that, like, a gang banger will get shot, or a truckload of soldiers will be blown up, nobody panics, because it's all "part of the plan". But when I say that one little old mayor will die, well then everyone loses their minds."

Ledger's Joker seems to sympathize with the soldiers, possibly due to past experience with the military. On top of that, supplying one of the most beloved comic book villains with a combat backstory wouldn't be off-brand for Dunkirk director Christopher Nolan.

While never confirmed, this theory is the epitome of "fanon." It's not canon, but fans generally agree that it's true.

However, a new theory on the character's presumed origins blows the old one out of the water. Reddit user the_fullest_bladder posted a two-sentence objection that sparked a couple hundred comments and nearly two thousand upvotes. In short: If The Joker was in the military, wouldn't his records show up in the GCPD's database when they ran his fingerprints?

Fellow theorists had plenty of ideas why this wouldn't be an issue: Maybe the police database wouldn't have access to military records? Maybe he burnt off his fingerprints with acid? Or maybe he was special ops and had to be deep undercover?

But one reply to the original Reddit post does something truly impressive. It casts a seemingly meaningless flash drive from the third movie of Nolan's trilogy into a whole new light. In The Dark Knight Rises, Batman uses the Clean Slate program, a computer program purchased by Wayne Enterprises, to bargain with Selina Kyle. Clean Slate allowed digital identities to be erased throughout the entire internet.

Why would Batman want this program in the first place? It would make perfect sense if a certain Clown Prince of Crime used it in the past and Batman wanted to limit the damage caused by concealing his enemies' identities in the future.

The program was given to Selina Kyle to ensure Batman's escape from Bane, but it was a steep price to pay. It inherently takes away all power by the GCPD to track villains and anyone else who could get their hands on Clean Slate.

It also happens to be a clever way to explain Joker's lack of a backstory. Clean Slate means that nothing can be ruled out-- maybe he was a soldier, maybe he was in Arkham Asylum, but no matter what, his past will remain a mystery. Just as the backstory of a cryptic villain should be.

The Dark Knight trilogy is streaming on Netflix until March 30.