Demeter is one of the six children of Cronus and Rhea. She the goddess of grain.
Demeter is primarily known for a story involving her daughter with Zeus, Persephone. The beautiful Persephone was stolen by Hades to be his wife. With her child missing, Demeter roamed the earth looking for her, abandoning her other duties. During this time, the crops would not grow, and humans and animals began to starve. Seeing this, Zeus stepped in to fix the situation. He sent Hermes down to Hades, ordering him to return Persephone. Hades said that he would gladly let her go. As she was leaving, however, Hades entreated her to eat a pomegranate. Persephone returned, and told her mother of her experience. Demeter grieved when she learned that Persephone had eaten a pomegranate, for the laws of Hades stated that Persephone now must return for good.. Upset, Demeter refused to let her daughter go. Needing to appease both of his siblings, Zeus reached an agreement. Persephone would stay with Hades for one-third of the year, a time which would become winter, and with Demeter for the rest.
The death and rebirth of Persephone in this tale was the central myth of the Eleusinian Mysteries, a cult especially popular in Athens.
The Romans identified Demeter with their God Ceres, a fertility goddess of the earth.
Burkert, Walter. Ancient Mystery Cults. Harvard Press, 1987.