WARNING: Spoiler alert! Please do not continue if you have yet to see Batman v Superman.
Batman v Superman: Dawn of Justice revealed that the Justice League would have to defeat the villainous Darkseid in the next film, as teased in Batman's dream sequence.
According to Birth.Movies.Death, Darkseid will play a crucial role in the film, but he will not be the main villain the Justice League will have to overcome. Steppenwolf, a relative of Darkseid, will actually be the Justice League's biggest antagonist.
Check out this Justice League featurette below:
While it might seem like a random choice, you have to realize that this is only a rumor. So don't read too much into it until we get an official confirmation.
However, it would truly explain this deleted scene from Batman v Superman, which Warner Bros. released a while back:
You can very clearly find Steppenwolf looking like his comic book self. Does this mean that Lex Luthor wasn't talking about Darkseid toward the end of the film, but Steppenwolf instead?
Rumor also has it that Darkseid will appear later in the movie, as a means to bridge Part One and Part Two, as well as other DC films.
Director Zack Snyder's Justice League: Part One hits theaters November 17, 2017.
[Source: Birth Movies Death]