Okay so recently there have been a lot of crazy DCEU theories. For example, Joker is Jason Todd, the dead robin. Another example is that Ben Affleck's Batman is Deathstroke. Well I'm here to shove another crazy theory down your throat.
oh I'm not gonna kill ya
Recently, Jared Leto stated that “I always get the sense that The Joker may be much older than people think. It’s something different. If you don’t break rules, you’re not going to strike new ground. I think I’ll be cooling down for the rest of my life.”
This can mean multiple things, 1. He is just stating that this Clown Prince of Crime is older than the previous Jokers to appear on screen.
Here's the pitch, in the recent Batman comics (#38 I believe) It is revealed that Joker is an immortal. Centuries ago he stumbled upon a chemical-filled meteorite which gave him immortality.
There are two other beings in the DCU that possess this power, Ra's al ghul, and Vandal Savage.
It is explained that The Lazarus pit contains the chemical that is contained in the meteorite. And Vandal Savage stumbled upon another meteorite as well.
However, I believe this theory is not completely out of the box. An immortal Joker would sure as hell be a different take on the Psychopathic clown, and if you read above, Jared Leto stated that his Joker will be much different than previous incarnations.
This could also explain possibly how the new Joker is so ripped, like look at the guy.
He's 43 going on 44 and he's got this body?
Another thing that stands out is this Clown prince of crime's wardrobe. This version of the Joker wears Arkham branded sweatpants, no shirt, and a purple snakeskin coat, not to mention the tattoos. This could be a Joker who evolves with the generation. Nobody in this time is as well dressed as they were back then.