According to this article, it is indeed Steppenwolf, later seen in Justice League.
If you’ve seen Justice League, you’re now well aware that the baddie that finally brings this team of superheroes together is none other than Steppenwolf. Indeed, instead of going with a major comics name or a character we’ve seen before in the DC Extended Universe, director Zack Snyder and his team opted to bring Steppenwolf (voiced by Ciarán Hinds) into the fold as the villain who squares off against Batman (Ben Affleck), Wonder Woman (Gal Gadot), Flash (Ezra Miller), Cyborg (Ray Fisher), and yes, Superman (Henry Cavill). But you may still have some questions after seeing Justice League about who Steppenwolf is, exactly, where he came from, and what he wants. So let’s break it down.
In the DCEU, Steppenwolf was first teased in a deleted scene from Batman v Superman: Dawn of Justice, which was released online at the time of the film’s release. We saw that when Lex Luthor (Jesse Eisenberg) was captured by authorities inside the Kryptonian ship, he was communicating with Steppenwolf via some sort of hologram-infused Kryptonian Skype. When the authorities arrived, Steppenwolf’s shape disappeared—but it was clear something was going on.
His background is not elaborated on in the movie, but in the comics, he was Darkseid's uncle and lieutenant.
But what’s the baggage here? Why is Steppenwolf so mad? The film doesn’t offer a ton of context to Steppenwolf’s actions beyond insinuations that he’s trying to impress alien supervillain Darkseid, who was teased as the DCEU’s potential BIG Big Bad in those “Knightmare” scenes in Batman v Superman.
Indeed, in the comics Steppenwolf is Darkseid’s uncle and a member of Darkseid’s Elite, which is a band of warriors who do Darkseid’s bidding. His role in the comics is basically doing anything that will make Darkseid happy or save his life—at one point Steppenwolf fought off the monstrous Doomsday, who appeared onscreen in Batman v Superman as the creature that Lex created in that Kryptonian goo....