The hierophant stood at the top of the priestly structure that ran the Eleusinian Mysteries, the initiation rites conducted at Eleusis in honor of Demeter and Persephone, and the office's defining feature was not simply seniority but exclusivity: it was reserved, for the entire attested span of the Mysteries' operation, to the Eumolpidae, an Athenian genos, or hereditary clan, tracing its descent from the mythical Eumolpos, said to have helped establish the rites themselves. Unlike many Greek priesthoods, which rotated, were elected, or were purchased for a fixed term, the hierophant held the office for life once appointed, and the position passed within the same restricted lineage across many centuries of continuous practice, from at least the sixth century BCE, when Athenian state involvement with Eleusis is well attested, until the sanctuary's eventual closure in late antiquity.
The name itself, hierophantes, "one who shows sacred things," describes the office's central function directly: the hierophant's central duty during the climactic night of the Greater Mysteries was to reveal, to initiates who had undergone the required preliminary stages, the cult's central sacred objects and, in most scholarly reconstructions, some kind of climactic vision or revelation understood as the rite's ultimate content. Ancient sources are consistent that the hierophant's ritual authority rested specifically on being one of the very few people permitted to know and perform this revelation, an authority the office's hereditary, single-clan structure was built to protect and control.