The word “oneiros” (plural: oneiroi) translates to “dream” in ancient Greek. In mythological tradition, the oneiroi were typically depicted as the sons of Nyx (Night) and sometimes associated with Hypnos (Sleep).

The most famous account comes from Ovid’s Metamorphoses, wherein three main oneiroi are described: Morpheus, who could take human form in dreams; Icelus (also called Phobetor), who appeared as animals and monsters; and Phantasos, who took the form of inanimate objects. These dream daimons were said to pass through gates of horn (for true dreams) or ivory (for false dreams) to reach sleeping mortals.

The Oneiroi exemplify that the cosmology of dreams is culturally specific, as is the relationship between the dreamer and the dream realm.

Daimons and Geniuses are often depicted as intermediaries between man and the divine, and similarly as threshold guardians between man and nature. This recontextualizes dream as a force of nature, the state of unconsciousness (per the Romantics) being one of man in union with the sublime.