Demeter is intimately associated with the seasons. Her daughter Persephone was abducted by Hades to be his wife in the underworld. In her anger at her daughter's loss Demeter laid a curse on the world that caused plants to wither and die, the land became desolate. Zeus became alarmed and sought Persephone's return. However, because she had eaten while in the underworld Hades had a claim on her. Therefore, it was decreed that Persephone would spend four months each year in the underwold. During these months Demeter greves her daughters absence, and withdraws her gifts from the world, creating winter. Her return brought the spring.
Demeter is also known for founding the Eleusinian Mysteries. These were huge festivels held every five years. They were importaint events for many centuries. Yet, little is known of them as those attending were sworn to secrecy. The central tenant seems to have been that just as grain returns every spring after its harvest and wintery death, so too the human soul could be reborn after the death of the body.
Dionysus is the son of Zeus and Semele. He is the only god to have a mortal parent. Zeus came to Semele in the night, invisable, felt only as a devine presence. Semele was pleased to be a lover of a god, even though she did not know which one. Word soon got around and Hera quickly assumed who was responsible. Hera went to Semele in disguise and convinced her she should see her lover as he really was. When Zeus next came to her she made him promise to grant her one wish. She went so far as to make him swear on the River Styx that he would grant her request. Zeus was madly in love and agreed. She then asked him to show her his true form. Zeus, was unhappy, and knew what would happen but, having sworn he had no choice. He appeared in his true form and Semele was instantly burnt to a crisp by the sight of his glory. Zeus did manage to rescue Dionysus and stiched him into his thigh to hold him until he was ready to be born. His birth from Zeus alone conferred immortality upon him.
Dionysus problems with Hera were not yet over. She was still jealous and arranged for the Titans to kill him. The Titans ripped him into to pieces. However, Rhea brought him back to life. After this Zeus arranged for his protection and turned him over the mountain nymphs to be raised.
Dionysus wandered the world actively encouraging his cult. He was accompanied by the Maenads, wild women, flush with wine, shoulders draped with a fawn skin, carrying rods tipped with pine cones. While other gods had templaces the followers of Dionysus worshipped him in the woods. Here they might go into mad states where they would rip apart and eat raw any animal they came upon.
Dionysus is also one of the very few that was able to bring a dead person out of the underworld. Even though he had never seen Semele he was concerned for her. Eventually he journeyed into the underworld to find her. He faced down Thanatos and brought her back to Mount Olympus.
Dionysus became one of the most important gods in everyday life. He became associated with several key concepts. One was rebirth after death. Here his dismemberment by the Titans and return to life is symbolically echoed in tending vines, where the vines must be pruned back sharply, and then become dormant in winter for them to bear fruit. The other is the idea that under the influence of wine, one could feel possessed by a greater power. Unlike the other gods Dionysus was not only outside his believers but, also within them. At these times a man might be greater then himself and do works he otherwise could not.
The festivel for Dionysus is in the spring when the leaves begin to reapper on the vine. It became one of the most important events of the year. It's focus became the theater. Most of the great greek plays were initially written to be performed at the feast of Dionysus. All who took part writers, actors, spectators were regaurded as scared servents of Dionysus during the festivel.
Eris is unpopular and frequently snubbed as a guest by the other gods and mankind. This was not always a safe thing to do. The most dramatic example being the Trojan War, which was an indirect result of not inviting Eris to a wedding.
His name is the basis for the word "panic". There are two differing explanations for this. The first is that he was present when Zeus defeated the Titans and claimed that it has his yelling that caused the Titans to flee. However, this seems at odds with his being Hermes son. The second is that he created the noises in the woods at night the scared travelers.
The Fates are old and predate the gods. It is not entirely clear how far their power extends. It is possible that they determine the fate of the gods as well. In any case, not even the most powerful is willing to triffle with them.