Demeter was the Goddess of Corn and therefore also harvest. She was the daughter of Cronus and Rhea and thus Zeus' sister. Along with Dionysus (also Bacchus, God of wine) Demeter was one of the two most important gods in the everyday lives of people. While most other gods did little to help people and people would have done much better without them, even when they were not outright harmful; these two were truly mankind's best friends. What also made them very different from other gods, was that they were the only two to have known and felt suffering and true grief, while the other gods lived happy blissful lives.
Demeter's tragic story is her search for Persephone. Persephone was Demeter's only daughter; Zeus was the father, Persephone was abducted by Hades and later returned to earth with the condition that she spends four months of each year with Hades. In these months Demeter misses her daughter so much that she withdraws her gifts from the earth, and winter comes. But when her daughter returns, Demeter is so happy that she restores all her gifts and spring starts.
One of Greece's most important and interesting festivals was associated with Demeter and in fact held in her honor. This celebration of harvest was held every five years for nine days in September. The festival included processions, sacrifices, dance, song and all other kinds of general rejoicing common to such festivities. But we know little about the most important part, the Eleusinian Mysteries, since all the participants vowed never to reveal what they have witnessed. Although some limited accounts do exist, and many different theories have been presented. This mysterious part of the festival was held in Eleusis, a small town not far from Athens.