The latest one is that Joaquin Phoenix is in talks to play Lex Luthor - one of the Man of Steel's main rivals.
Luthor isn't confirmed as the main villain in the sequel yet - though hints in the first film make his entrance seemingly inevitable.
Though Phoenix looks like a frontrunner, he's not the only person rumored for the part.
Luthor also isn't the only antagonist people are speculating about.
We wouldn't be surprised if there was another villain also introduced in the sequel.