There are many creatures in the mythology, folklore, and fiction of many cultures who are one-eyed, this page lists such one-eyed creatures.
In mythology, folklore and religion
Arimaspi, legendary people of northern Scythia, "always at war with their neighbours" and stealing gold from griffins. They had a single eye in the centre of the forehead.
Balor, a giant in Irish mythology, with one eye in his forehead that would wreak destruction when opened
Bungisngis, one-eyed giants of Philippine folklore
Cyclopes (singular: Cyclops), one-eyed giants in Greek mythology, including Polyphemus. They had a single eye in the centre of their forehead.
Polyphemus, a giant Cyclops shepherd in Greek mythology
Fachan, a creature from Celtic mythology with one eye, one arm and one leg
The Graeae, the three witches (or sisters) that shared one eye and one tooth between them; often depicted as clairvoyant. They were forced by Perseus, by stealing their eye, into revealing the location of Medusa.
Hagen or Högni, a Burgundian warrior in German and Norse legend, depicted as one-eyed in some accounts
Some yokais, in the Japanese folklore, have a single giant eye:
Hitotsume-kozō, monsters (obake) in Japanese folklore, with a single giant eye in the center of the face
Hitotsume-nyūdō could pass for really tall human priests if not for the large, single eye in the center of their faces.
Kasa-obake, one-eyed sentient umbrella yokai of Japanese folklore
Jian, a bird in Chinese mythology with only one eye and one wing. A pair of such birds were dependent on each other and inseparable.
Kabandha, a demon with no head or neck with one large eye on the breast and a mouth on the stomach. Kabandha appears in Hindu mythology as a character in the Ramayana.
Likho, an embodiment of evil fate and misfortune in Slavic mythology
Mapinguari, giant sloth-like cryptid of Brazil and Bolivia often described as having one eye
Odin, a Norse god (he was born with two eyes, but traded one for a drink from Mimir's well)
Ojáncanu, one-eyed giant with a ten-fingered hand, a ten-toed foot, a long beard and red hair of Cantabrian mythology who embodies evil, cruelty and brutality
Rell, a cyclops in the film Krull. The Cyclops traded with the Beast one of their eyes for the ability to see into the future. The Beast did give them the ability to see into the future – but they can only see the moment of their own deaths.
Sauron, the eponymous arch-villain of The Lord of the Rings, often depicted as looking through a single 'Eye' in Peter Jackson's cinematic adaptations of Tolkien's work
Kyle, the owner of the Queen's Goiter, and Cloppy, Evan's one-eyed monster doll from The Barbarian and the Troll
Anime and manga
Lord Boros, in One-Punch Man, the alien leader of the Dark Matter Thieves, self-proclaimed subjugator of the universe, and the first antagonist to give Saitama a "serious fight"
Norman Burg, the butler and weapons specialist to Roger Smith in The Big O
Iwanaga Kotoko, in In/Spectre, A 17-year-old Goddess Of Wisdom to the spirits and humans alike, has only one eye and one leg due to sacrificing a part of her to become a goddess.
Wotan/Wandrer in The Ring of the Nibelung, a Germanic variant of Odin in Wagner's cycle of four music-dramas
Black Shuck - a one-eyed demon dog in the song Black Shuck, by rock band The Darkness from their debut album Permission to Land.
Other
Alastor "Mad-Eye" Moody, the Auror in the Harry Potter series by J. K. Rowling. He has one normally functioning eye, and one magical eye that can see through magical cloaking.