The mircale of modern medicine holds the potential for phenomenal improvements in the human physique. But also, the sceptre of dreaded side-effects, as well. The more well known Rex Tyler of Earth-Two knew this well, for when he invented Miraclo and digested its contents, he opened his life to a world of adventuring as the Hourman... and some misery! The rush of power became to addictive, much like that which his counterpart on Earth-One, Multiplex, experiencing when requiring atomic energy to super-charge his ever duplicating cells.
For the young lad who would one day become Master Man, however, there seemed no such threat to his personal heallth. In order to cure himself of ailments as a toddler, a mystery physician had him ingest the Vitacap, which permenantly endowed him with superhuman abilities. Comparable to Hourman and Multiplex in the superstrength, endurance, and speed department, Master Man quickly detached himself from society as he moved to a mountaintop headquarters. Coming back down to Earth-S only to clean up its human filth, his career was rather shortlived. Perhaps, just like Hourman, he was beginning to experience the negative effects to his unnatural state of being, as possible his Vitacap finally drained his mythical might. Or perhaps, like the Man of the Hour, he was called away to a battle from which he never returned (although Rex returned from his brief voyage to Earth-X, averting near tragedy). Alas, the mists of time conceal the true answer to this mystery.