In Greek mythology, the Cyclops is a creature, like a giant, with a single eye in the center of its forehead. This monocular creature showed in several myths and stories, from Hesiod's Theogony to Homer's Odyssey, often filling the role of a minor villain in whatever capacity the story needed. Sometimes depicted as barbaric of brutish, it was rare to find them depicted in a good light, although the tribes of cyclopes were know to raise sheep, and some were prized as builders, such as when the built the Cyclopean walls of Mycenae and Tiryns.
This role as a minor villain for the creatures has extended to Castlevania where the creatures, more often than not, stand as guardians of their respective areas. Inconveniences for the heroes that had to fight them, the massive brutes could prove formidable in battle but generally weren't featured in the same way as other monsters in the armies of Dracula. Certainly the Cyclops isn't thought of at the same level as, say, Carmilla or Death.
Probably the Cyclops's biggest claim to fame was in its first appearance, in Castlevania III: Dracula's Curse, where it stood as the area guardian who also protected the status of Sypha Belnades. Curiously, here the cyclops is also given the ability to turn creatures to stone when he defeats them, as in the case of Sypha, which is a power more often ascribed to Medusa. Still, this encounter did leave a mark in the memories of fans, with this being the key moment that players think of when talking about the Cyclops (even though he showed up in a few other games since).
Fighting Against the Cyclops
Once the hero (or heroes, if the player elects to have Grant DaNasty tag along with Trevor Belmont) reaches the statue garden that acts as the current resting place of Sypha, they encounter the Cyclops. For the most part the Cyclops will walk back and forth across this arena, damaging the hero when he touches them. Avoiding the damage, or tanking the hit, while layering on damage against the Cyclops is the easiest strategy, although that can be easier said than done. Note that while the Cyclops will largely seem to ignore the hero, just pacing back and forth, it will strike at the heroes with his giant hammer if they get too close, or do a dashing charge at the heroes if they get too far away.
Curiously there is a secret way to damage the beast in this game. With the dagger, thrown from one of the top blocks in the arena, the heroes can throw the dagger across the screen. If it strikes the middle of the room at the same time the Cyclops passes underneath, a lightning bolt with strike down, dealing a quarter of the boss's health bar in damage.
The beast appears again in Castlevania III, one stage later, as the guard at the end of the Ghost Ship. This is actually a two-part boss as a spirit animated the dead from within coffins. First the spirit brings out two mummies for the heroes to fight, and this is the immediately followed (in the same encounter, without a chance for healing) by the Cyclops. The basic fight is exactly the same, you're just already in a weakened state from the previous encounter with the mummies (plus all of the stage leading up to it) so this can seem like a much more difficult fight even if all the basics of it are the same as with the previous Cyclops encounter.
And this whole encounter that shows up a third time, a couple of stages later, as the mummies and the cyclops are paired up, this time with a third beast, a giant demon. The cyclops portion of the encounter remains unchanged but now you have to worry about your health and ammo consumption even more as the demon will come out after the cyclops in killed, dragging out this battle even further. As if that wasn't bad enough, this triple threat encounter is essentially unavoidable as you'll find it not only on Sypha's path, but also on the path you'd take in the game with Alucard, too.
The Cyclops returns as an optional boss in Castlevania: Harmony of Dissonance. Here his fight is similar to the Castlevania III encounter, although the giant is now much more quick and agile. He'll strike out with his hammer, dealing massive damage if you're unlucky enough to get caught under it. He also has his dashing attack once again, and this time he has the speed and power to traverse the whole room despite its length. It's good to come in prepared if you want to fight this boss and earn his prize (a Heart Max Up), but be wary of the amount of damage it can lay out because that will pile up quick.
After this game, the Cyclops were reduced in prominence for their next two encounters: Castlevania: Lament of Innocence and Castlevania: Curse of Darkness. In Lament, the hero will actually encounter two Cyclopes in the Ghostly Theater, the Cyclops and the re-skinned Red Ogre. One beast has a club, the other a mallet, although they both fight functionally the same. Killing these two beasts is relatively easy -- just stay out of range of their melee strikes -- and defeating them actually opens up the way to the true boss fight of the area.
Finally, both the Cyclops and the Red Ogre return in Curse of Darkness, this time as regular (if potent) enemies. They again have their basic melee strikes but the Red Ogre also comes with a dashing attack as well as a grab-and-hold move that can be quite damaging. Also of note, there are two forms of the Red Ogre this time around, a weaker (level 48) version found in Castle Dracula, and a more power (level 75) version in the Tower of Evermore. This latter form is very strong and can prove to be a formidable foe for the unprepared.
Other Appearances of the Cyclops
In the secret are in level 4 of Castlevania Dracula X: Rondo of Blood the Cyclops appears as a background element. The player has no way to interact with the beast in any way (nor will it attack at the heroes), instead it's there in the background, steadily unloading blocks so it can build some kind of wall. That's a nice touch referencing the mythology of the creature.
Cyclops in Pop-Culture
As the first season of the Castlevania Netflix anime covers the period where hero Trevor Belmont collects his two allies, Sypha and Alucard (sorry Grant, Sir "Not Appearing in this Series"), the Cyclops makes one last appearance here, too. He once again guarding the statue of Sypha (along with other townspeople turned to stone by his gaze) and it's only after Trevor takes on the beast and defeats him that Sypha, and all the other people captured, are freed of the curse. It's noted that the Cyclops here "feeds on the fear of its victims trapped within their stone shells", which is a particularly nasty way to go.