Starting out as a recurring villain, Robin Mask soon became one of the most essential members of the Seigi Choujin (Justice Supermen) team. Robin wore knight-type armor made out of sapphire (later remade out of steel), and wearing the armor reduced his strength, giving his opponent a fair chance at beating him. Although Robin is only a few years older than most of the cast he is considered the veteran of the group and often comes up with the teams' overall battle plan.

In the anime he is depicted as wearing a blue undershirt underneath his armor, making it seem at times that he has blue skin.