Kerykes in Wikipedia
The Kerykes (Greek: Κήρυκες) were one of the sacred Eleusinian families of priests that ran the Eleusinian Mysteries during the Hellenic era. They popularized the cult and allowed many more to be initiated into the great secrets of Demeter and Persephone. Starting about 300 BC, the state took over control of the Mysteries, specifically controlled by two families: the Eumolpidae and the Kerykes. This led to a vast increase in the number of initiates. The only requirements for membership were a lack of "blood guilt" (meaning having never committed murder) and not a barbarian (i.e. Greek and able to speak Greek). Men, women and even slaves were allowed to be initiated.
Kerykes, which means in Greek heralds, were also part of the ritual and competitors at the Olympic Games (see Herald and Trumpet contest).