"Thaumas took as his wife Electra, daughter of Okeanos,
whose stream is deep, and she bore swift Iris..."
(Hesiod, Theogony, 265-266)
In addition, this passage in the Theogony goes on to state that Iris was the sister of the Harpies (Hesiod describes the Harpies as two "lovely-haired" creatures with "fast wings").
In Greek myth, the rainbow goddess primarily acted as the messenger of the Olympian gods and goddesses. Iris often served as Hera's personal messenger in many ancient sources - indeed, it is interesting to note that the famous Parthenon frieze shows Iris in close proximity to Hera. However, the poet Homer tended to portray Iris as the messenger of Zeus in his pair of epics called the Iliad and the Odyssey. In this respect, Iris shared her role as messenger of the gods with the Olympian Hermes.
Scholars have suggested that Iris, as the personification of the rainbow, represented an example of a brief union of earth and sky. The qualities of this natural phenomenon in turn influenced her role in myth as the goddess who delivered messages between the heavens and earth.
Who's Who in Classical Mythology