In Greek mythology Iris was the daughter of Electra and Thaumas and was the personification of the rainbow. Like the rainbow, she mediated between the heavens and the earth: her principal role was to act as messenger of the gods and goddesses in their dealings with humans. She's usually pictured with golden wings, like Hermes, and she holds a pitcher in one hand and a herald's rod in the other. Many ancient sources have her serving as Hera's personal messenger, though Homer tended to have her serving in a similar capacity for Zeus. Another of her duties was to lead the souls of dead women to the Elysian Fields, and as a token of this Greeks planted iris on the graves of dead women.
Iris is a genus of perennial plants of the family Iridaceae, which also includes freesias, crocuses, and gladioli. Irises are popular with gardeners because many types bear attractive flowers. Characteristically, the blooms have three petals called "standards" and three outer petal-like sepals called "falls". The "bearded" varieties of iris - mostly native to North America - have thick bushy beards on the falls, while the beardless varieties - mostly Asian - are cleanshaven. The irises I grew up with were tall with long sword-shaped leaves and large majestic purple flowers with yellow beards, but irises are a varied lot; some grow high and have big showy flowers in a range of colours, while others are dwarf varieties with small delicate flowers.
In general, irises are tolerant plants which grow well in their native habitat; they don't need a lot of fertilizing, but do like well-drained roots. Irises can grow from seed, but are more usually propogated by separating the root or rhizome into chunks, which you can do any time your irises seem to be getting crowded. Just pull up some of the rhizomes, thinning out the clump of irises, and plant them somewhere else.
Cultivated for thousands of years, iris rhizomes (orris root) have long been used as medicine and as perfume. Orris is a fixative which keeps colour and scent in things like potpourri. The iris may also be the origin of the fleur-de-lis, which does look kind of like a stylized iris.