In ancient Greek religion and mythology, Iris is a daughter of the gods Thaumas and Electra, the personification of the rainbow and messenger of the gods, a servant to the Olympians and especially Queen Hera. Iris appears in several stories carrying messages from and to the gods or running errands but has no unique mythology of her own. Similarly, very little to none of a historical cult and worship of Iris is attested in surviving records, with only a few traces surviving from the island of Delos. In ancient art, Iris is depicted as a winged young woman carrying a caduceus, the symbol of the messengers, and a pitcher of water for the gods. Iris was traditionally seen as the consort of Zephyrus, the god of the west wind and one of the four Anemoi, by whom she is the mother of Pothos in some versions.

A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.