The opening of “Man of Steel” on Krypton includes a wide shot of the planet, in which a destroyed moon is visible in the background. Years later, it’s now very clear what could have done that kind of damage. During a “Man of Steel” watch party hosted by VERO, Zack Snyder confirmed that the Easter egg was meant to set up Doomsday:
“You notice up there is the broken moon, which in the comic book, Laura, that moon was broken by – we all know who it was […] a long time ago by Doomsday, and so this Doomsday concept I wanted to plant early that Doomsday is a thing that exists and could be brought into this universe […] plant some little Easter eggs that allow us to harvest those ideas for later.“
Although the Doomsday we meet in “Batman v. Superman” is not the same one that destroyed the moon, Snyder’s blink-and-you-miss-it easter egg makes sense. A planet known for its obsession with controlling birth and death, Krypton testing the waters with cross-breeding does indeed track with their modus operandi. The scene pays homage to the source material while not tying down any strict origin for the villain. In fact, a comic-accurate Doomsday would have entailed telling an even darker past.