The title 'Hierophant' was constructed from the combination of ta hiera ('the holy') and phainein ('to show'). As such, his principal duty was, as his name indicates, to show and explain the sacred symbols and figures--perhaps in a kind of chant or recitative, as he was required to have a good voice. Encyclopedia Britannica
For two thousand years, the Hierophant of the Eleusinian Mysteries was so important to the ancient world that the image of him in his official robes is still our image of the holy father. The way our modern Pope dresses is still very similar to the images that exist of the Hierophant. There is a tarot card dedicated to The Hierophant that has come down through the centuries, which some modern decks have renamed, The Pope. We know the Hierophant showed the holy objects (the hiera), to the epopteia (those who see). He revealed the sacred mystery and announced the appearance of the gods Kore and Demeter. But how did he become a father?
According to Eunapias, who wrote The Lives of Philosophers and Sophists, in the 4th century, the last Hierophant in the long line to serve at Eleusis was such a visionary, he foresaw the overthrow of Eleusis and all the other temples and libraries. In short, he foretold the ruin of Hellenistic Greece. He predicted that after his own death, there would be a usurper Hierophant who had no right to be there because he was sworn to other gods, and that “in his lifetime the sacred temples would be razed to the ground and laid waste.” And that’s exactly what happened. This usurper Hierophant was “a pater in the ritual of Mithras.” These predictions were right, Eunapias said, and reported that the usurper was from Thespae.
According to some ancient writers (all of them Christian and therefore antagonistic to Eleusis), the Hierophant played the role of the king consort in sexual union with the goddess in a ceremony called the Hieros Gamos (divine marriage). Those early Christian writers claimed that what took place “in the dark” at Eleusis was “debauchery.” Tertullian denounced the “whoredom of Eleusis,” and Eusebius condemned the “unnamable rites of the mysteries” as “adulteries and yet baser lusts” (Walker 911). Since Eleusis was a fertility cult, it’s logical to assume the Hieros Gamos was about sex. I think it was the theatrical performance of a sacred ritual.
In the ancient Hymn to Demeter, King Celeus is married to Queen Metaneira, and father to Demophon and three daughters. While Demeter was grieving the loss of her daughter, she is found in the disguise of an old woman at the Well of the Beautiful Maidens by the daughters (the beautiful maidens). Out of pity, they take her home to their mother who takes her into her household as a nurse to her young son, Demophon. Later, Demeter is grateful and tells King Celeus to establish a temple to her at Eleusis. Celeus becomes one of the first Hierophants, and his family, the Eumpolpidae, become one of the founding families, those who can become Hierophants and Melissae. The Hymn to Demeter, among other things, shows how the ancient sacrificial kings could have become Hierophants after king sacrifice was ended, an idea in the story.