Everyone thinks they have an idea as to who the big baddie is going to be for the first part of Warner Bros. JUSTICE LEAGUE team-up to get the DC Cinematic Universe rolling in major fashion. But if you're initial guess here was Darkseid, you may be dead wrong. New rumors are circulating that while Darkseid may be involved somehow, he won't be the large threat that the band of superheroes face as they combine their efforts. Someone else has gotten the job.
SPOILER ALERT
According to Devin Faraci at Birth.Movies.Death, Steppenwolf is getting the nod. For those who might need to bust out their DC Encyclopedia to familiarize themselves with Steppenwolf, the character is the uncle of Darkseid and the military leader of Apokolips. And while that may sound cool on paper, Steppenwolf really didn't come into his own until The New 52 version of him was unleashed, allowing him to invade Earth and put up a bit of a fight, which sounds like what he might be doing here.
Darkseid had been alluded to in BATMAN V SUPERMAN: DAWN OF JUSTICE (look out for the Omega symbol in Bruce Wayne's dream, if you haven't already), and he'll be surfacing at some point in the next chapter, but don't expect him to really do anything as you had prior until most likely PART TWO.
JUSTICE LEAGUE – PART ONE is set for release on November 17, 2017.