Iris

Iris was the goddess of the rainbow and the messenger of the Olympian gods. She was often described as the handmaiden and personal messenger of Hera. Iris was a goddess of sea and sky--her father Thaumas "the wondrous" was a marine god, and her mother Elektra "the amber" a cloud-nymph. For the coastal-dwelling Greeks, the rainbow's arc was most often seen spanning the distance between cloud and sea, and so the goddess was believed to replenish the rain clouds with water from the sea. In myth, she appears as an errand-running messenger and was usually described as a goddess. Her name contains a double meaning, being connected with both the Greek word iris "the rainbow" and eiris "messenger."

"The thunder crashed and storms of blinding rain poured down from heaven. Iris, great Hera's envoy, rainbow-clad, gathered the waters and refilled the clouds." - Ovid, Metamorphoses 1. 270 ff (trans. Melville) (Roman epic C1st B.C. to C1st A.D.)

"Soaring to heaven on balanced wings, [Iris] blazed a rainbow trail beneath the clouds as she flew... Iris, glory of the sky, cloud-borne." - Virgil, Aeneid 9. 2 ff

"And the rain's comrade, the bow of Iris, wove her many colours into a rounded track, and shone bent under the light-shafts of Phaethon [Helios the Sun] opposite, mingling pale with dark, and light with rosy." - Nonnus, Dionysiaca 2. 200 ff (trans. Rouse) (Greek epic C5th A.D.)