Multi-millionaire Simon Stagg is trying to create a worker who can be altered to work in any environment and is smuggling illegal mutagens to do so. A broken vial of the mutagen causes a train crash which Green Lantern manages to avert. While doing so he meets former military buddy Rex Mason, who is working for Stagg and is romantically involved with Stagg's daughter Sapphire. When Rex quits to marry Sapphire, Simon objects and secretly uses Rex as an unwilling guinea pig for his "Metamorpho" experiment. A mutated Rex learns Stagg was responsible but Simon claims Green Lantern set him up. Luring GL into a trap, Rex uses his metamorphic powers to knock him out and closes in for the kill.
Metamorpho Metamorpho first appeared in DC Comics in Brave and the Bold #57 (December 1964). Always considered somewhat of a freak, he originally rejected an invitation to join the Justice League (in Issue #44, original series), but had his own series eventually and joined their JL's Europe branch. His origin here is substantially different - in the comics he gained his abilities and freakish appearance from the mystical Orb of Ra. However, the whole Sapphire/Simon Stagg backstory is basically the same. The original hardluck freak/mutant hero, Metamorpho has died and been brought back a couple of times, sometimes with little or no explanation (like in his recent Doom Patrol appearance).