Doomsday is heavily rumored to appear as the main villain in Batman vs Superman: Dawn of Justice. Rumors suggest that Lex Luthor experiments on Zod's dead corpse and his body reanimates into what we know as Doomsday.
Fans have been divided on Doomsday being featured in Batman vs Superman and also why Zod turning into Doomsday doesn't hold much water and is not faithful to source material. But this theory I will suggest to you guys might make a lot more sense.
Kryptonian born warriors
In Man of Steel the children of Krypton are genetically engineered to make them a more efficient race. Krypton population follows a certain Guild from which they are chosen from and grown at birth. The Guilds are the Warrior Guild, Thinker Guild, Mediator Guild, Artisan Guild and the Laborer Guild. As we all know Zod, Faoroa and etc. belong to the Warrior Guild in which they were bred to be Kryptonian warriors that serve Krypton.
Now Zod's heritage as a kryptonian who was specifically bred into being a warrior has a Doomsday genome due to Betron experiments on all kryptonians warriors and imbue them with Doomsday genetics as a fail safe just in case things went wrong.
And why non-warriors like Jor-El or Kal-El don't have the Doomsday genome in there DNA at all.
Which would explain Zod's invulnerability and why he can't be broken down so easily when Lex does experiment on his dead corpse and eventually turns into the creature we know as Doomsday. And probably during the process of reanimation the last thing he remembers is who killed him which would be Superman, and goes on an all out rampage and only mission is to find Superman and kill him.
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