Cyclopses are one-eyed giants. They are very big, strong, and are considered to be ugly by most people, be they humans or even monsters.
Depiction from the Books
Majority of Cyclops are offsprings of sea god Poseidon, thereby making them Percy Jackson's relatives (half-brothers. One such a notable individual is heroic Tyson). They have radar-like auditory and can mimic any voices perfectly.
The first generation of Cyclopes were raised by Ouranos and Gaea. But Ouranos was not pleased with the appearances of monsters and imprisoned them until Kronos overthrew him. Even under Kronos' rule, Cyclopes were not freed so Kronos' mother Gaea, his son Zeus, and his wife Rhea plotted against him. Cyclopes are discarded by their parents when they are born (with the exception of Polyphemus) so they are left to fend for themselves. They mostly live in human cities and are treated as outcasts or mistakes. Because of conditions these species are subjected for their upbringings they mostly go astray. No one wants them and they end up growing wild on streets.
Cyclopes are also feared or avoided even by most monsters, as even when they are young, they are still incredibly strong. Tyson, when he was a baby Cyclops, unknowingly frightened away other monsters, leading to Percy not being attacked all year.
The Lightning Thief
A Cyclops is depicted as a a tall man in a trench coat and hat who kept stalking on Percy Jackson (or tried to keep close eye on Percy).
The Lost Hero
Sump, Torque, and Ma Gasket are evil Cyclopes family who prey on demigods. They take great pride of belonging to Hyperborean (Northern) Cyclopes since they are the meanest of the brethrens. Northern species of Cyclopes often interact with Roman demigods. Additionally Hyperborean Cyclops are not of Poseidon's descendants. The three Cyclopes are slain by Leo Valdez and Tyson.
The Sea of Monsters
This novel features a hostile Cyclops named Polyphemus, a large, greedy and blind Cyclops who stole Golden Fleece to enrich himself and his own island residence. Polyphemus also had been using the fleece to lure Satyrs to their deaths. In this book Percy discovers that the majority of Cyclopes are his half-siblings (sharing the same father). Because Polyphemus is also son of Poseidon, Percy Jackson is unable to kill him in spite of bluffs. With Golden Fleece secured, Percy and his companions escape from Polythemus' Island, but Clarisse La Rue makes mistakes of taunting Polythemus. The Cyclops, using her voice as a guide as radar detecting its target, threw a rock at Percy's gang and sank their ship. Luckily, Percy and Tyson call up Rainbow and his friends to carry them away from the island. As they are moving away, Percy hears Polyphemus gloating about how he finally sank Percy's gang. Percy hopes that he never finds out that he is wrong.
Polyphemus belongs to Southern Cyclopes: They seem to be not as smart as Northern Cyclopes since they don't use their building talents and instead herd sheep. But beware. They maybe sheep herders but much like their Northern cousins, they also often eat heroes and demigods and are typically malevolent beings. The Southern Cyclopes often interact with Greek demigods.
The Cyclopes are minor antagonists in the 2013 movie Percy Jackson and the Olympians: The Sea of Monsters.
They are portrayed by Derek Mears and Aleks Paunovic.
Seven years before the beginning of the story, Annabeth Chase, Luke Castellan, Grover Underwood and Thalia Grace tried go to Camp Half-Blood while being pursued by two Cyclopes. When they had almost reached the camp, one of the Cyclopes threw a tree at them, injuring Grover. Luke helped him and Thalia decided to stay to hold off the Cyclopes, who went after her. She managed to wound one of them in the leg, but the other grabbed her and threw her away. As she lay dying, her father Zeus turned her into a pine tree, creating a magical barrier around the camp. The two Cyclopes went to attack the others before they entered in the camp, however they were stopped the barrier and tried to break it, without success.