His backstory is that in spite of his jealousy and resentment, Zor-El listened when Jor-El claimed Krypton was doomed. Using Brainiac-based technology he built a dome around Argo City, and a space rocket to send Kara to Earth just in case Argo's force-field failed. He did not warn his wife and daughter about his plans, though. Minutes before the explosion he put his daughter to sleep, laid her on a space pod and blasted her into space. Argo City outlived Krypton but not for long. Without a way to sustain themselves, all Argoans eventually died. Zor-El was the only left when Brainiac found the city. Brainiac turned Zor-El into a cyborg, erased his memory and reprogrammed him to serve him.