The late 60s were not a good time for the Superman books, and I find myself skipping over a lot of issue. But Superman 205 (April 1968) has some significance worth pausing for.
Binder and Plastino introduce Black Zero, an alien murderer who has come to Earth. The panels meant to evoke fear over this new character I find kind of amusing, really.
Black Zero is more than happy to brag to Superman about his great achievement, destroying Krypton. According to Zero, he came there to kill everyone, only to learn about Jor-El’s theory about the planet exploding. He checked it out himself, but found that the reaction had stopped. So, he started it again, and made sure the planet blew up.
This is not the significant thing. We only have Black Zero’s word for these events, and no real reason to trust him. At any rate, this story was never referenced again.
The rest of the story does not question his claims either. Instead, it’s all about stopping Black Zero from destroying the Earth. Jax-Ur pleads successfully with Superman to be allowed out of the Phantom Zone to help him, as he is just as mad as Superman about Zero destroying their planet. But Jax-Ur gets shot with red kryptonite, which causes his body to transform into a snake.
Superman finds and takes care of Black Zero’s anti-matter bomb. Jax-Ur changes again, to a Medusa-type creature, and turns Black Zero to stone. Superman intends to keep him, but Jax-Ur smashes Black Zero to bits, to ensure he never finds a way to become human again.
While the character of Black Zero never returns, the name does. It will be given to various people and groups associated with Krypton. And that’s why I wrote about this story.