A minor Easter egg in The Batman hints at a shared universe with Todd Phillips' Joker, but it proved to be little more than a cruel trick, as the two movies exist in purely separate universes. Matt Reeves' The Batman introduced one of the most successful cinematic incarnations of the Dark Knight to the screen by making use of gritty, grounded realism fused with a gothic noir atmosphere. Borrowing elements of Christopher Nolan's Dark Knight trilogy and introducing added originality into its approach to its story, The Batman is by far one of the most successful Batman movies of all time.
Interestingly, The Batman is somewhat similar in tone to Todd Phillips' Joker. Joker's massive success stemmed from similar reasons to The Batman's: it told a more grounded version of the iconic character's established story in a rich and self-contained world free from the more fantastical elements of other superhero movies. This particular trend in adapting Batman characters has proved a hit with critics and audiences alike, and it's something that draws distinct parallels between The Batman and Joker.
The Batman contains a single Easter egg that seems to connect it to Joker, but it's actually a cruel nod to the popularity of Phillips' film. The Batman's incarnation of the notorious Arkham Asylum is named the Arkham State Hospital, and the only other time that name has been used is in Joker. Though this implied a shared universe between The Batman and Joker, Reeves' final tease of Barry Keoghan's Joker dispels any notion that the crossover was ever possible. This made the use of Joker's name for the Arkham institution a particularly cruel Easter egg, because it briefly built hopes for the best possible shared Batman universe only to dash them shortly after.
Could Joker & The Batman Ever Have Worked Together?
The way in which the Arkham State Hospital is used in The Batman proves that Todd Phillips' Joker was never going to have formed a shared universe. The name implies a connection, but the hospital is then used to introduce an entirely new iteration of the Joker, establishing Reeves' world as entirely separate from Phillips'. The fact that Barry Keoghan's Joker appeared in a deleted scene that would have established him earlier in the movie confirms that the shared universe wasn't seriously considered, because it would have dispelled the notion much earlier in The Batman.
There are other reasons why The Batman and Joker couldn't have co-existed, though. Joker's story sees an older Arthur Fleck become the iconic villain, and he even meets a young Bruce Wayne. The timeline that this implies would have made Phoenix's Joker far too old in comparison with Pattinson's Batman, presenting a significant logistical barrier to connecting the two grounded Batman universes with anything more substantial than the Arkham State Hospital's name.
Although The Batman's Easter egg implies a connection to Joker only to destroy all hopes of a shared universe, it's still a clever reference. It's a subtle way of establishing parallels between the two realistic incarnations of Batman's world, and though there's no deeper meaning to it, it's a clever nod to Phillips' movie. With The Batman introducing Barry Keoghan's Joker, any shared universe with Todd Phillips' Joker has been rendered impossible, making the Easter egg seem particularly cruel - despite how clever it is.
