How does Joker fit in with the Batman universe?

Not least the fact that Batman himself appears in the movie…

Is Batman in Joker?

Well sort of, yes. At a couple of points in the narrative we meet young Bruce Wayne (who later becomes Batman), first when Arthur visits Wayne Manor and tries to force the sombre young Master Wayne into a smile (until he’s stopped by butler Alfred, played by Douglas Hodge), and again later when the well-trodden death of his parents (see below) plays out onscreen.

However, it’s Bruce’s father Thomas who plays a larger part in the story. He appears first as a candidate for Gotham City mayor who whips up unrest over the city’s inequality, and later ties into Arthur’s storyline more directly when the wannabe stand-up believes Thomas to be his real father.

In an odd twist, this would have made Joker Batman’s half-brother – though the film later reveals that this backstory was a fantasy of his mother’s, who used to work for the Waynes and adopted Arthur later on.

Are there Batman Easter Eggs in Joker?

A few, though not quite as many as you might think. Obviously characters like Thomas and Martha Wayne, Alfred and Bruce Wayne appear in the movie, and Batman’s famous origin – where his parents are gunned down in Crime Alley, inspiring him to lead a life of vigilantism – appears towards the end of the film.

Within that origin, two crucial details also appear that tie the death of the Waynes to the comics and other cinematic interpretations. Firstly, the film the family are seeing before they get mugged – 1920’s The Mark of Zorro – has been included in Batman’s origin since 1986, when Frank Miller wrote it into his seminal comic The Dark Knight Returns (previously, it was just noted that the Waynes were walking home from a movie).

Another detail in Joker– the cascading broken pearls of Bruce’s mother Martha – also memorably appeared in that comic-book miniseries, and this has become a trademark element of the death scene appearing in nearly every screen incarnation of the story including 1989’s Batman, 1995’s Batman Forever, 2005’s Batman Begins, TV series Gotham and 2016’s Batman vs Superman among others.

There is a slight change to this scene, however, with the Waynes’ deaths characterised as part of a larger riot taking place in Gotham inspired by Arthur’s clown persona, whereas in other media it had been presented as a one-off crime.

Other callbacks to classic Batman comics include the mental hospital Arthur and his mother were previously admitted to, named Arkham after the prison/asylum where most of Batman’s victims ended up, and Arthur’s dreams of becoming a stand-up comedian (above), which are shared by the man who would become the Joker in Alan Moore’s classic (and controversial) comic The Killing Joke.

And of course, Arthur’s appearance and name as the Joker are taken directly from Batman's arch-nemesis, albeit with a slightly more grounded feel.

Will Joaquin Phoenix’s Joker appear in the Robert Pattinson Batman movies?

Almost certainly not - despite recent comments by Joaquin Phoenix that he might fancy a sequel, Joker has been billed as a one-off character study centred on the iconic clown super-villain, and is not intended to tie in to the wider franchise even if there are more movies starring the character.

With that in mind, it’s no surprise that Joker director Todd Philips has said Joaquin Phoenix’s version of the character will “definitely not” appear in director Matt Reeves and star Robert Pattinson’s forthcoming Batman reboot.

"We made this movie, I pitched it to Warner Bros. as one movie. It exists in its own world. That's it," he said.

And he probably won’t appear in any other films either, despite Phillips initially seeming open to the idea.

“I would do anything with Joaquin Phoenix, any day of the week,” Phillips said in August.

“There’s nobody like him. If he was willing to do it, and if people show up to this movie, and Warners came to us and said, ‘You know what? If you guys could think of something…’ Well, I have a feeling that he and I could think of something pretty cool.”

However, the director later walked back these comments, describing reports of a possible Joker sequel as "annoying".

"We have no plan for a sequel," he told press after a screening.

"The quote was, 'I will do anything Joaquin wants to do.' And I would. But the movie's not set up to [have] a sequel. We always pitched it as one movie, and that's it."

Still, you never know. If Joker is as big a hit as some suspect, and Joaquin Phoenix is keen to take on Robert Pattinson’s Batman, perhaps we haven’t seen the end of this version of The Clown Prince of Crime after all…

“You know, I wouldn’t have thought about this as my dream role. But now, honestly, I can’t stop thinking about it,” Phoenix said on American talk show Popcorn with Peter Travers.

“I talked to Todd [Phillips, the director] a lot about what else we might be able to do, in general, just to work together, but also specifically, if there’s something else we can do with Joker that might be interesting.

“So, it ended up being a dream role. It’s nothing that I really wanted to do prior to working on this movie."

He continued: “I don’t know that there is [more to do].

“Me and Todd would still be shooting now if we could, right? Because it seemed endless, the possibilities of where we can go with the character.”

Joker is in cinemas now