In Batman v Superman, we got to see Victor Stone's transformation into Cyborg with the help of his father and a mysterious living box of alien origin. To comic book fans, there was a strong possibility that this peculiar artifact could be a Mother Box, an artifact created by the New Gods, Darkseid's race, whose abilities include controlling reality and technology — and they were right!
In the scene in question, a dismembered Victor Stone being treated by his father in S.T.A.R. Labs, becomes the host of a shapeshifting box, which attaches itself to the ex-football star and makes him Cyborg. Speaking to Entertainment Weekly, Zack Snyder said:
“That’s the first glimpse of the Mother Box there. It was an agonizing birth.”
These devices are called "Mother Boxes" due to their complete protection and nurturing by their host. This makes sense, considering Cyborg's ability to communicate with technology and the boxes' ability to control it.
“I really wanted to show Cyborg’s birth because I feel like he plays such a strong part coming up, and I really wanted to give a sense of him. I really want [the audience] to know how far he’s come.”
Cyborg will be played by actor Ray Fisher in the upcoming Justice League: Part One, which premieres on November 16, 2017.