Zod is a really, really, REALLY truly evil bad guy. He's like the Kryptonian equivalent of Skeletor, or those little plants that pop out of the tubes and eat you on Mario.
Jar-El (Superman's dad) condemned Zod to the Phantom Zone, which is also a main part of the Superman movies. At the start of Superman it shows General Zod and the other two people being sent into the Phantom Zone, and on Superman 2, the blast from the Nuclear Missile which Supes throws into Space shatters the prison that Zod and them were trapped in, and they get out and cause havoc on Earth for about 2 hours and 15 minutes.
The Vanishing is a world that was created in the Phantom Zone, and thus, General Zod is there.
There's some more to it than that, but I think you have to kind of piece it together on your own, and interpret it in your own special way. I mean, I've got my own way of seeing it, but if I say it, then I'm afraid someone will jump in saying, "OMFG U IDIOT WATS RONG WIT U!!!!!111"
But even if you're not majorly a big fan, you can still kind of get it. 🙂
Oh yeah, Superman also killed a pocket universe's General Zod, when he and his two cronies escaped from The Phantom Zone and murdered everyone on Earth.😘
When he was captured Zod swore that he would find a way to Superman's Earth, and that he would kill everyone there just as he did on his Earth.
Superman believed him, and since he was the only "law" left on Earth he sentenced them all to death by Kryptonite (since he was from a different universe the K didn't affect him).
This was the universe where the
"protoplasmic" Supergirl is from.
Zod's spirit is supposed to be alive (he inspired The General's attack and obsession with Superman) so it looks like this guy might be the real deal.