Zarrko is an evil scientist from the future, born in Old New York of the peaceful 23rd century of an alternate future. Zarrko was once a civil servant, but built a time machine to escape from his time and visit more primitive periods, like United States in the 1960s, where nuclear weapons could be stolen easily, as he sought to become a conqueror and dictator in his own time. Zarrko stole an experimental cobalt bomb to use in his own time during its test, thus taking over the Earth which had no nuclear weapons, but was pursued by Thor using his hammer and a piece of metal from the ship to travel to Zarrko's time. Thor gained access to Zarrko's base after distracting the tyrant by getting someone to impersonate him, and defeated his robot servants even after they got his hammer. He recovered the bomb when Zarrko dropped it towards the Future City and caused Zarrko's ship to crash land using a storm he had summoned with his hammer.