Ever since the first promo image of the Suicide Squad 's Joker (Jared Leto) first surfaced courtesy of director David Ayer there's been a lot of discussion about the merits (or lack thereof) of this version.
The reaction was largely negative, which is understandable given the radical change to his looks and the uncharacteristic teeth and tattoos. Leaked set photos have shown us that he actually looks better with his shirt on, which is something.
There's already been a ton of different versions of the Joker, both on screen and in the comic books. The comic book Joker has usually skirted the darker side though; shooting Barbara Gordon and taking pictures of her bleeding naked body to torment Jim Gordon with in The Killing Joke; beating Robin (Jason Todd) to death in A Death In The Family; having his face surgically removed to wear as a mask in the New 52 Detective Comics and topping it off, his physical abuse of Harley Quinn and pretty much everything else he does in Death Of The Family.
In terms of this article, it's important to keep in mind that when I say Leto could be the darkest Joker yet, I mean this in terms of the character's live-action iterations, not including the comic book versions. (As I said above, that's a hard act to beat.)
The Jason Todd Storyline
There's been a ton of rumours swirling regarding whether or not the Joker will feature in [Batman v Superman: Dawn of Justice](tag:711870), with Leto rumoured to appear in a flashback scene chronicling the death of Jason Todd (the second Robin).
In the comics Joker brutally beats Jason to death with a crowbar; an action which has long standing psychological effects on Batman, leaving him believing that he had failed to protect his family. There's nods to this in the Batman v Superman trailer. Well, less of a nod than an outright reference.
Robin's suit appears in Bruce Wayne (Ben Affleck)'s collection, scrawled with graffiti mocking Batman's inability to save him. This means that, even if we don't directly see the event, Joker did kill Robin in the DCCU canon. The fact that Batman didn't even clean the graffiti off the suit means that he's keeping it as a momento of his failure; a failure that has deeply affected the troubled, broken Batfleck that we see in the trailer.
The Physical Abuse of Harley Quinn
The Suicide Squad trailer gives us a new origin for Harley Quinn, showing Dr. Harleen Quinzel strapped to a table as the Joker stands over her. His line at the end of the trailer, "I'm not gonna kill ya, I'm just gonna hurt ya. Really really badly" is directed at her, and those electroconvulsive therapy tools do not look pleasant.
This keeps in line with the violent nature of the relationship between Harley and the Joker that has persisted through her run in the comics but is particularly prevalent in the New 52 continuity, which the DCCU is trying to keep more or less in line with. It's suggested then that, rather than Harley falling in love with the Joker when she meets him at Arkham, she's one of his victims in a much more explicit manner than we've seen before. Certainly it's the first time we'll have seen such a violent and controversial relationship between them in a live-action setting, and it could be tough to watch.
The leaked set photos have also shown an altercation between the two of them as Harley still appears as Harleen. In alternating shots they kiss, she holds a gun to his head and he slaps her. Hard.
The Psychological Torment of Batman
Okay, we have seen this in the movies before - especially during Heath Ledger's turn in The Dark Knight. It's a central facet of the Joker's personality after all, but it's really ramping up in the DCCU now and will be a contributing factor to the events of Batman v Superman.
The letter Bruce receives in the Batman v Superman trailer mocking him for failing to save his employees when Wayne Tower collapsed is likely another jab from Joker, similar to the graffiti on Robin's suit, as part of the psychological torment he lays out for Batman. The accusation that he failed to protect his family doesn't just apply to the death of the parents but also to the death of Jason Todd, who had a familial relationship with Bruce, and here the deaths of his employees - indirectly caused by the battle between Superman (Henry Cavill) and General Zod (Michael Shannon) in Man of Steel.
It is this sense of failure and responsibility that seems to be the driving force for the conflict in Batman v Superman, so regardless of whether or not Joker actually makes an appearance, his presence will still be felt regardless.