Who is Brainiac in Superman?

Brainiac is the notorious space outlaw that shrunk cities such as Kandor and in general went about doing evil and getting into battles with Superman. He (this was revealed much later) is actually a robot or an Android- why then didn't Superman destroy him with a blast of heat vision- as this would not be taking life I often wondered about that. Apart from a comic space monkey, Brainiac has no companions. If Superman got him alone with his fields down- why not- Zapp! Lex Luthor is a human being, but Brainiac is not. I often wondered why Superman just didn"t zap him.