Birds of Prey stars Margot Robbie as Harley Quinn, reprising her role from Suicide Squad. Suicide Squad co-starred Jared Leto as The Joker, but since then, we've seen an entirely different Joker character on the big screen in the form of Oscar winner Joaquin Phoenix. So which version of the clown prince of crime was really being considered when the new film sees Harley Quinn break up with him?
As it turns out, the answer is really none of the above. While there have been numerous Joker characters over the years, and two just within the last few, Director Cathy Yan recently told Yahoo that she didn't really think about who Harley Quinn was breaking up with, because ultimately, it wasn't important. According to Yan...
For me it mattered less, actually. It didn’t really matter which version of it. We pull as much from Suicide Squad as we did from version of the Joker in comic books as well. And we kind of kept it vague. Because it’s really not about him, you know? It’s about her.
There are some pretty clear references to Suicide Squad in Birds of Prey, beyond the fact that Margot Robbie is playing Harley Quinn, we see a wanted poster with Jai Courtney's Boomerang on it, which Harley calls out. We also get some flashback scenes in the new movie that were in Suicide Squad first, showing Harley's transformation at the hands of Joker.
Having said that, we never actually see Joker at any point, and ultimately, all the aspects of Joker that we learn about in Birds of Prey are fairly standard to the character, so it could be that Birds of Prey isn't, strictly speaking, connected to Suicide Squad at all.
In the end, it seems clear that Birds of Prey simply didn't want to deal with all the baggage that came with "cinematic universe" storytelling and so instead focused simply on telling the story the filmmakers wanted. By keeping things generic and general, anybody else who cares to can come and take characters like Harley Quinn and Joker forward in whatever way they want, and Birds of Prey won't be a hindrance to that.
This is just another element of the muddying of what we previously referred to as the DC Extended Universe. While the three movies to feature Superman had a clear through line, and Suicide Squad made a direct connection to them, since then the entire concept has seemed to lose favor. Even the upcoming The Suicide Squad, which will feature several actors and characters from the previous film with a very similar name, has seen people involved hesitate to call it a sequel.
In the end, as Cathy Yan says, it really doesn't matter. Birds of Prey is still a great movie, no matter which Joker is only vaguely part of it.