Zoanoids

Zoanoids are genetically-altered human beings who can assume the form of powerful, horrific monsters (what their monstrous forms look like is apparently dependant upon the individual). Originally, the Zoanoids were created as warriors for the aliens who created mankind, but after the aliens left the Zoanoids went into hiding. They are ruled over by a single Zoanoid, called the Zoalord, and their sole aim is to take over the world using the Guyver. Although it is assumed that most Zoanoids are born Zoanoids, an ordinary human being can be turned into one by being put through a special process developed by the Chronos Corporation (and if the process is incomplete, the individual suffers an agonizing death upon their first, unbidden transformation).