The Cyclops are humanoids, and the original inhabitants of the planet where O-Parts Hunter takes place. Normal humans are descendants of space travelers. The Cyclops have long since hidden in their village, but are now coming into the open.
Unlike Cyclops' in ancient Greek mythology, Cyclops in O-Parts Hunter have two normal eyes, and a mark on the forehead. The mark will only open into an eye for a few Cyclops and grant them with incredible abilities. Other differences with normal humans include skin and hair color: So far all Cyclops have had white hair, and a brown/greenish skin. Since O-parts are the weapons of the space travelers, no Cyclops O.P.T.s exist.
Even while their ancestors were forced to hide from humans, the current generation bears no grudge against humans, recently making Jio Freed the village leader and starting trade routes with other villages for supplies and such.
Human/Cyclops crossbreeds can exist, often taking after one of the parents, having either human or Cyclops skills. A mixed child does have a human skin color, however. Not very much is known about Cyclops/human relations, expect that it's discouraged by the Cyclops people, possibly because of the tragedies that follow after human/Cyclops couples have children such as Arcaido, who killed 90% of the world population after dominating the world, and Kujaku, who killed his own father, the brother of the village mayor.
The third eye that is on the forehead of a cyclops can be used only when it is open. It's power is strong as it can control objects that it can see.