Hero Factory/WMG

Heroes are repurposed civilians

 * Heroes aren't built completely from scratch. Most villains canonically started out as something different, so it's possibly that Heroes are civilian workers that, either voluntarily or otherwise, have been reworked into a body more suitable for crimefighting and world-saving and whatnot. Sure, there are mentions of Heroes being built "from scratch", but it's implied that the Assembly Tower is how Mak Megahertz "recovered" from being de-atomized.