Parentage:
She's the daughter of Thaumus, a sea god, and Electra, a cloud nymph. Her siblings include the Harpies and Arke, goddess of the second rainbow.
Consorts & Children:
Through her husband Zephyrus, the west wind, she's the mother of Pothos ("yearning"), one of Aphrodite's Erotes (gods of love and sex).
Notable Stories Involving Her:
As goddess of the rainbow, she's usually depicted as either the personification of the rainbow, or as a young woman with golden wings. During the Titanomachy, she sided with the Olympians while her (fraternal) twin sister Arke acted as messenger for the Titans. In addition to being a messenger for the gods, Iris also acts as Hera's handmaiden.
Sacred Symbols:
Her symbol is, of course, the rainbow, but so too are irises and the blooming iris of the fleur-de-lis. Her attribute is a pitcher she carries around that contains water from the river Styx, which she uses to put to sleep those who perjure themselves.
Iris Around the World:
The Romans identified her with Arcus, but other, similar deities include the Greek Hermes, the Norse Heimdallr, the Mayan Ixchel, and the Zulu Mbaba Mwana Waresa.
SOURCES: Greek Mythology.com, Encyclopedia Mythica, & Wikipedia