This summer we got the chance to meet Dwayne Johnson's version of the antihero Black Adam when he had a cameo in DC League of Super-Pets, but his real premiere is in October when Black Adam premieres in theatres on October 21.
Most superhero movies these days seems to have some kind of post-credits scene, often setting the stage for a sequel or something similar, and it seems like this won't be any different. As DC and Warner are doing test screenings, we now know that there is one for Black Adam as well, and according to several reports, it connects the character to the wider DC Extended Universe.
Normally, you want to make a splash with these post-credit scenes, so a reasonable guess would be that one or several very famous DC characters show up. As Black Adam is incredibly powerful, we could imagine him meeting something in the line of Gal Gadot's Wonder Woman, or even Henry Cavill as Superman.
Also, as Justice Society of America is in the movie, it wouldn't be too far-fetched to think that previous members such as Green Lantern or The Flash could show up as well.
Thanks The Hollywood Reporter