As has been clear from the beginning, Joker is not part of the DCEU whatsoever, with Joaquin Phoenix’s Joker not intended to be a recast version of Suicide Squad‘s Jared Leto but an entirely different incarnation of the Clown Prince of Crime altogether. That being said, there are a couple of small details that create a connection to the movies of Warner Bros.’ mainstream DC franchise.
First of all, near the beginning of the film, a news broadcast on TV mentions rumors of “Super Rats” appearing in Gotham’s sewers. This sounds like an oblique nod to Otis Flannegan AKA Ratcatcher, a minor Batman foe from the comics who has the ability to communicate with and control rodents. Given the obscurity of this character, it’s interesting that he should get his first on-screen mention in Joker. Soon, however, a gender-flipped version of Ratcatcher will appear in The Suicide Squad, as played by Daniela Melchior.
Secondly, Joker ends with the fated death of Thomas and Martha Wayne. As always, the wealthy family exit a movie theater before being killed by a crook in an alleyway. As you probably noticed, there are a bunch of posters adorning this theater, including one for Excalibur.
Funnily enough, Excalibur was also one of the movies playing at the theater seen at the beginning of Batman V Superman: Dawn of Justice, which also recounted the Waynes’ murder. So, we can presume that, in both instances, young Bruce lost his parents in the year Excalibur was released: 1981.
Again, Joker clearly isn’t set in the same continuity as the DCEU, but these two easter eggs create some sort of link with the franchise, perhaps establishing that it’s all part of the same multiverse if not the same universe.
