Christopher Reeve starred in Superman & Keaton’s Batman shares a Universe.

Source: Twitter
Christopher Reeve, a celebrated American actor, is best known for playing Superman in the 1978 film and its three sequels. Today, 44 years ago, the Superman movie was released in theatres.
SUPERMAN premiered 44 years ago today, so here’s a great moment from the film: Christopher Reeve takes off his glasses, straightens his posture, and transforms into the Man of Steel in front of our eyes. pic.twitter.com/lRIR3peij8
— All The Right Movies (@ATRightMovies) December 10, 2022
Since the 1960s, DC Comics has dealt with multiverses; the classic tale Crisis on Infinite Earths was an (unsuccessful) attempt to combine all of DC comics into a single, unified one.
According to Bleeding Cool, the Superman films by Christopher Reeve and Michael Keaton’s Batman movies take place in the same DC universe due to the recently released Dark Crisis: Big Bang. In particular, Superman and Supergirl are the only superpowered heroes on Earth in Earth-789, the universe in which the Joker murdered Batman’s parents.

Despite its mention, the Michael Keaton/Christopher Reeve movie universe isn’t the subject of Dark Crisis: Big Bang. The one-shot comic book is intended to depict Dark Crisis on Infinite Earths’ aftermath. Pariah, the Infinite Earths series’ significant character from the original Crisis, The 2015s events Convergence storyline, which reversed many of the Flashpoint storyline’s events, is undone when Pariah revives the DC multiverse in the Dark Crisis series. If you haven’t noticed by now, there is a lot of retconning and re-retconning in the DC Comics universe.
Dark Crisis: Big Bang mentions other great iterations of the heroes than the ones starring Michael Keaton and Christopher Reeve. The comic also refers to Earth-66, a world in which Batman and Robin battle “exceptionally benign enemies.”

Of course, Dark Crisis: Big Bang mentions several other continuities. The list of alternate realities also includes the Michael Keaton and Christopher Reeves universes. The New 52 universe, the Gotham by Gaslight steampunk universe, the Superman: Red Son alternate reality where Superman turns into a communist after moving to the Soviet Union, and the Jurassic League dinosaur universe. Strangely, a few well-known programs, such as the universe of Batman: The Animated Series and the Christopher Nolan Batman films, don’t feature on the list.