At first I was very iffy about the role of the Joker in "Suicide Squad." However, he could be the one character to resurrect the DCCU, or DC cinematic universe. How exactly is this one character who was in this movie for about a total of ten minutes going to save the DCCU as whole? Well, the answer to that isn’t as clean cut as it seems.
Now, for the first aspect of this answer, let’s look into the background of the character The Joker. There are considered to be three jokers from the three ages of comic books; the Golden Age (1938-1950), the Silver Age (1956-1970) and the Modern/Bronze Age (1970-now). Putting it in cinematic perspective, the first joker that was displayed on the silver screen was portrayed by Cesar Romero who played the part of the Silver Age Joker. He was playful and did not focus on killing people. This is due to the fact that during the Silver Age, the Comic Code Authority stepped in and put a stop to violence in comic books. The next Joker who was played by Jack Nicholson was that of the Golden Age. He was much more violent than the Silver Age Joker and did not care about killing people left and right. The final Joker that was displayed before Jared Leto’s rendition was the Modern Age Joker who was played by the late Heath Ledger. This version is much more psychotic and pays attention to the fun side of being insane. Now the big question here is, which Joker does Jared Leto follow in the footsteps of? The answer to that is simple. He follows the exact path of the classic Golden Age Joker. He was a relentless killer, he was not so batman-centric as the modern age joker is, and he was also portrayed as a mob boss or having close ties to organized crime.
For the next few elements of this answer, we are going to take a dive into the heart of the DC comic books. DC is known for introducing the use of multiple and parallel dimensions. Following the canon of the comics, there are actually infinite earths in which different variations of your favorite heroes and villains all live. When I say variations, I mean that it could range from our normal run-of-the-mill Batman on one Earth to a Batman who is a pirate on a different Earth. This is mentioned not only in the comics, but in the television show "The Flash" as well. There was also a multiverse crossover between the other two DC shows, "Supergirl" and "Legends of Tomorrow." This has been confirmed by the show-runners and writers for the franchise that both the television and cinematic universes coexist.
So how does the idea of the multiverse relate to the Joker? Essentially, DC is cultivating to do a massive crossover between the DC universes since this movie helped confirm the fact that there are different versions of the Joker even though Jared Leto followed the classic Golden Age Joker persona. It seems as if they are aiming to play the DC ultimate card which is to do a crisis event. This theory is further driven to the fact that in "Batman vs. Superman: Dawn of Justice" where it was shown that one of the future big villains that the superheroes will fight is Dark Side. He is a villain who is infamous for being able to travel from universe to universe with ease.
DC is lining up the perfect set up to do a Crisis event that happens in the comic books. In a time where DC is taking a major loss due to the fact of the very low ratings of their movies, following through with the Crisis event could be the one thing to revive the whole DC franchise.
For more information about this theory, Matpat did an excellent job explaining this in full detail at his YouTube channel, The Film Theorists.
