[quote=Abysse]
Who even is superboy prime, besides a massively overpowered superman copy?
[/quote]

he is Superman from another universe that erased by an insanely powerful villain known as Anti Monitor, he survived but eventually went insane and became possibly one of the greatest threats to the DC universe.

He also lost everyone he cared about which is why he hates the DC heroes because he views them as not deserving to exist.