Chione, daughter of Boreas and Oreithyia, had a son, Eumolpus with god Poseidon. The fact that Eumolpus was the fruit of an illegitimate affair frightened Chine so she threw her baby into the ocean. However, Poseidon rescued the baby and took special care of it in Ethiopia. When Eumolpus grew up, he married the daughter of the king of that country and had a son named Ismaros. Yet, Eumolpus attempted to rape his wife's sister, a fact that enraged her father. To avoid punishment, Eumolpus went in secret with his son to Thrace and asked for shelter at Tegyrios, king of Thrace. Tegyrios received them in his kingdom and later he let her daughter marry Eumolpus' son, Ismaros. However, Tegyrios fearing of Eumolpus who might wanted to overthrow him from the throne, forced Eumolpus to go to Attica where the latter developed strong ties with the Eleusinian rules.
When Eumolpus heard about the early death of his son, Ismaros, he went again to Thrace in order to take the throne. Later, the Eleusinian people asked for help from the king of Thrace to fight together the Athenians. According to Thucydides, the first historic event of the city of Athens was the siege of the Acropolis by king Eumoplus and the Eleusinian warriors. During this war, Eumolpus was killed by the hand of Erectheus, king of Athens, a fact that enraged god Poseidon, who took revenge by exterminating all the members of Erectheus' family. From that time, Eleusis was subject to Athens and kept its privileges as a great place of worship. According to other version of the myth, not only Eumolpus but also his son Ismaros died in the war against the Athenians, so Keryx, another of his sons, was left alone in Eleusis (according to others, Keryx was son of Hermes and Aglaulus, daughter of the Athenian king Cecrops).
Nevertheless, the most prevalent traditions have it that Eumolpus was the first man to be initiated in the Eleusinian mysteries and that his descendants, the Eumolpidae, had the exclusive privilege of performing the Eleusinian mysteries.