Greias (Greek Γραῖαι, the "elders," the "gray ones") are characters from Greco-Roman mythology. They were three sisters who had gray hair from birth. They were the sisters Dino (Δεινώ, "fear"), Enius (Ἐνυώ, "horror"), and Pericardius (Πεμφρηδώ, "alarm"), daughters of Phocis and Ceto and sisters of the Gorgons, with whom they were often confused. All three together possessed one tooth and one eye, of which they alternately served themselves.
Charged with guarding the path that led to the dwelling of the Gorgons, they were tricked by Perseus when he set out to kill Medusa. The hero managed to get hold of his one eye, so that the three of them fell asleep at the same time and he could perform his deed without danger.
According to another version, Perseus had taken their eye and tooth and refused to return them unless the old women directed him to the nymphs who would provide him with the means to defeat Medusa: winged sandals, a kind of satchel, and the helmet of Hades.
In the Percy Jackson and the Olympians series by Rick Riordan, the sisters are introduced as cab drivers in New York City.
In the House Of Night series, these are three friends who belong to the "Daughters of Darkness" group.