Brainiac. Lex investigates and studies the events of Superman. He owns Zod's ship, Zod's body and other krypton in tech left behind. On Zod's ship, they key used to override Jor-el is actually the brainiac key. Brainiac, knowing that Superman's existence breaks kryptonian law, informs Lex on how to destroy Superman. In a compartment on the ship is a Doomsday vessel (egg or whatever you choose to call it) that needs kryptonian dna to bring it to life. By using Zod's dna, being that he was exposed to the sun and absorbed its energy, that power was transferred into the doomsday creature. After Lex's failure to destroy Superman, Brainic creates a vessel for himself to become the flesh and metal villain that we all know. The two reasons that make me believe this is that Lex knows a lot more about kryptonian tech than he should and the bot floating behind him when he says "if man won't kill God, the devil will do it." Hoping it's something similar to this.