It is interesting, and perhaps significant, that the story of Iphigenia's sacrifice is not mentioned in the Iliad or the Odyssey, despite there being ample opportunity and reason to do so. The earliest source for the story is in the report we have of the lost Homeric Cypria (which is usually thought to date one to two centuries after the Homeric epics). In the next source, Aeschylus' play The Libation Bearers (c. 460 BCE), Clytemnestra, the wife of Agamemnon, mentioned the killing of Iphigenia as part of her justification for killing Agamemnon upon his return to Mycene after the Trojan War. The two plays of Euripides, Iphigenia at Aulis, and Iphigenia at Tauris, are centered on the story of Iphigenia. The story also gets minor mention in Hesiod's Catalogue of Women and Eoiae 71, which reports that she was changed into the goddess Hecate instead of being sacrificed.
The complexity of Iphigenia's story is present in many of the heroines of Greek mythology. Many of them appear either to have been goddesses in earlier times--which powers they have lost in the historical period--or are so similar to known goddesses that they appear to be hardly more than a different name for the same divinity. Iphigenia is so closely associated with Artemis, that her name is frequently seen as a mere epithet for Artemis (H.J. Rose p. 119.), which justifies the suspicion that Iphigenia might have originally been another competing virgin goddess of the hunt, whose character and functions were subsumed by Artemis.