Cyclops

The Cyclops is a one-eyed enemy beast with pointy ears in Castlevania. They have hammers and very slow and can be hurt by hitting the eye.

Dracula's Curse
Cyclopes made their first appearance in this game. They're purple and hold green hammers. One's responsible for turning Sypha into a stone, guarding her statue until Trevor Belmont and Great Dynasty defeated it.

Several other Cyclops bosses teamed up with other bosses, like the Mummies and Leviathan.

Cyclopes are found only in the Locations 3, 4A, 7 and 7A.

Wai Wai World 2
Cyclopes made their second appearance in that game with horns. They're also considered as Onis, usually translated as Ogre.

They are found only in Location 9.

Rondo of Blood
The Cyclops appeared without a hammer and has a ponytail in this game.

They're found only in Location 4.

Harmony of Dissonance
The Cyclops is blue and has a red eye in this game and appears as a boss. This enemy is quicker and stronger and execute jumping and dash attacks in the game.

Lament of Innocence
There are only two Cyclopes in this game, the original one with a club and the Red Ogre. The Cyclops is now pale blue, instead. The Red Ogre has tatoos on it. They appeared in several locations.

Curse of Darkness
The Cyclops made its latest appearance in the game. The Cyclops is purple, instead of blue, while the Red Ogre is has no tatoos.

Other variants
Red Ogre: A Cyclops found only in two games.

Other media
The Cyclops was supposed to appear in the animated movie version of Dracula's Curse. It looks much more like a gorilla.