In Greek mythology, Eumolpus (also Eumolpos) was the son of Poseidon and Chione (or Hermes and Aglaulus).
According to Apollodorus,
Eumolpus was an excellent musician and singer; he played the aulos and the lyre. He won a musical contest in the funereal games of Pelias. He taught music to Heracles.
During a war between Athens and Eleusis, Eumolpus sided with Eleusis. His son, Himmarados, was killed by King Erechtheus. In some sources, Erechtheus also killed Eumolpus and that Poseidon asked Zeus to avenge his son's death. Zeus killed Erechtheus with a lightning bolt or Poseidon made the earth open up and swallow Erechtheus.
Eleusis lost the battle with Athens but the Eumolpides and Kerykes, two families of priests to Demeter, continued the Eleusinian mysteries. Eumolpus' youngest son, Herald-Keryx founded the lines.