Intergang, with quiet, secret assistance from Lex Luthor.
Corben wasn't a monster any more than he was a respectable officer and gentleman, and became an Intergang enforcer with some standards, and is in personality largely a professional type; his grudge against Lois is rather tame, for instance, as he doesn't believe in taking things personal . Then he "got" sick like in STAS, and got a body that merged hardware supplied by Apokilips, left over Brainiac Tech, and stolen STAR Labs tech, with a software control system coded by Luthor... and no sensory perception beyond audio/visual, unless someone else gives him a sensory program of some kind. He's still mostly sensible, but in extreme distress and trauma.
I think "man tricked into perpetual sensory derivation" is more maddeningly sympathetic than "punk crook as Terminator" *and* "Military man turned into bad guy by his government #5."