Phantom Zone
Superboy first meets another human survivor of Krypton, Klax-Ar, a villain who claims he destroyed the planet, in "Superboy" #67 (1958). Three years later, both the Phantom Zone and its most infamous occupant, General Zod, make their first appearances in "Adventure Comics" #283 (1961), in a story that features Superboy accidentally trapping himself in the Phantom Zone after a cache of dangerous Kryptonian weapons arrives on Earth. Zod and other Phantom Zone villains would become recurring villains in Superboy stories, and go on to plague Superman.