A really interesting character is introduced by Hamilton, Swan and Klein, and it’s a shame that World’s Finest 158 (June 1966) is his only appearance.
Robin and Jimmy Olsen are out exploring when they find three Kandor-like bottles in a cave. They appear to be exactly like Brainiac’s bottled city. The boys bring them back to the Eyrie and decide to enter one an investigate.
When the boys don’t come back, Superman and Batman get on the case. They find the bottles, and enter them. In each they find a hostile and violent culture, and are lucky to escape, and rescue the boys when they find the right bottle.
These bottles were populated by Brainiac A, a rebellious earlier model that was exiled by the Computer Tyrants of Colu when he refused to collect cities for them. He decided to capture evil cities instead.
I have always really liked this story, and wish that the character had returned to face his successor in some tale.