Phobetor, also known by his true name Icelus, was one of the Oneiroi, the personifications of dreaming. He is also the triplet brother of Morpheus, the god of dreams, and Phantasos the god of surreal dreams or fantasy. Phobetor was the personification of nightmares and appeared in dreams in the form of animals or monsters in order to frighten those who would be unfortunate enough to welcome him into their minds as they slumbered.
Phobetor is the son of Nyx, the primordial goddess of the Night, with Erebus, the embodiment of Darkness. Phobetor had the ability to appear in the mortal realm in the guise of various animals and could change their physical forms at will in order to interact with mortals in the waking world.
Phobetor has no true physical form even though there are various sculptures of him where he is presented as a humanoid winged daemon. Even so, this was mostly the closest thing to Phobetor having a true physical form. In nightmares, Phobetor would continuously shift into numerous forms, ranging from earthly animals to nightmarish beasts. When he takes the form of the animal it is usually to give the person that is dreaming a sense of ease as they relax in their slumber, but when he becomes a monster, the human is immediately plunged into a state of terror.