Steppenwolf is the primary antagonist in Justice League, though his relationship with the ruler of Apokolips, Darkseid, may have been changed drastically for the movie. In the comics, Steppenwolf is Darkseid's uncle.
Geek Magazine has revealed that Steppenwolf will actually be Darkseid's nephew, meaning the roles have been reversed in the movie. There's no saying if this change will really affect the events in Justice League, or the planned sequel which is expected to see Darkseid assume the role of the villain. An excerpt from the magazine reads:
“In Justice League, Batman and Wonder Woman, following Superman’s death in battling Doomsday, is intent on bringing together a team to take on Steppenwolf. This new menace is the nephew to Darkseid of Apokolips (presumably the big bad of the second JL adventure). Steppenwolf is on Earth to retrieve three Mother Boxes, one of which is now a part of Cyborg.”
There is indeed a chance that the magazine got their facts wrong and meant to say Darkseid is Steppenwolf's nephew, but if that's not the case then the dynamic between the two characters will definitely be different from what comic fans have grown accustomed to.
Opening Nov. 17, Justice League stars Ben Affleck as Batman, Henry Cavill as Superman, Amy Adams as Lois Lane, Gal Gadot as Wonder Woman, Jason Momoa as Aquaman, Ezra Miller as The Flash, Raymond Fisher as Cyborg, Willem Dafoe as Vulko, Jesse Eisenberg as Lex Luthor, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, Connie Nielsen as Queen Hippolyta, Amber Heard as Mera and J.K. Simmons as Commissioner Gordon.
(via Screen Rant)