New Olympians are the descendants of the beings of Greek mythology, now dwelling on the hidden island of New Olympus.
The New Olympians were originally known, in the time of ancient Greece, simply as Olympians. They originated as the offspring of Children of Mab by mortals of various species (including "lower" animals), which accounts for their various unusual (by human standards) features.  Some were worshipped as gods, while others were believed to be monsters, and consequently feared and mistreated (among the latter was the Minotaur, Taurus's ancestor).
The Olympians finally became so embittered towards humans for so often persecuting them that they decided to withdraw themselves from the world. They left from various Mediterranean locales for the island of New Olympus, to shut themselves away forever. In the course of their departure, they invited the local gargoyle clans to join them. Some of the gargoyles went to New Olympus with them, but others remained in the outside world, hoping that they could yet peacefully co-exist with humans.  Exactly when this event took place is unknown, although in light of some Roman-influenced elements of New Olympian society (such as the Senate - a Roman institution, the Columnadium - which name is clearly Latin-influenced, and Jove), it presumably took place at some point after the founding of Rome (traditionally dated to 753 B.C.). New Olympus had definitely been sealed off from the outside world by the time of Caesar Augustus (27 B.C. - A.D. 14), for Elisa has been described as the first human to visit New Olympus in 2000 years.
Here the New Olympians, as they now called themselves, settled down to a certain amount of peace. But even their society was not without frictions. By the present day, it had produced one notorious criminal, the shape-shifter Proteus, who caused considerable havoc and even murdered Taurus' father, who was then Chief of Security, before becoming imprisoned. The New Olympians continued to (for the most part) hate humans and view them with considerable suspicion, although at the same time, they were uneasily aware that eventually the humans would discover them; New Olympus was protected by a cloaking device, but it could not withstand the developing human technology for long. The New Olympians also used their technology to monitor transmissions made by humans. 
In 1996, Goliath, Elisa, Angela, and Bronx came to New Olympus on the Avalon World Tour. The New Olympians were alarmed at Elisa's presence on the island, and, fearing that she would lead others of her kind there, quickly imprisoned her. Goliath decided to break her out of prison, but Proteus, who had learned of the situation, tricked Goliath into freeing him, planning to then destroy New Olympus and make his escape. Elisa helped Taurus, who had become Chief of Security by then, recapture the treacherous shape-shifter, however, and thus showed him and the other New Olympians that not all humans were evil. The New Olympians gave her her freedom, and allowed her to leave the island with her friends. ("The New Olympians")
In the future, Terry Chung will come to New Olympus just as Elisa had done, and his visit will serve as the final catalyst for the New Olympians to reveal themselves to the outside world.  Taurus, Talos, and Sphinx will promptly go to New York and present their credentials at the United Nations Building, beginning diplomatic relations with humanity.  Following this event, three factions will develop in New Olympian society, each one having a different attitude towards New Olympian-human relations. Some, such as Ekidna, will be firmly isolationist.  Others, such as Sphinx, will want to make peace. A third faction, led by Jove, will be in favor of ruling over the humans, and being worshipped as gods by them once more. By 2198, relations between New Olympus and the outside world will be tense but peaceful. Indeed, in 2198 the leader of New Olympus will join the other world leaders on Queen Florence Island and subsequently be taken captive by the Space-Spawn. 
New Olympians come in so many different forms that it is impossible to provide a description for an overall "norm". Some look part-human and part-animal, such as Ekidna, Kiron, Sphinx, and Taurus. Others look reasonably human, but with other unusual traits, such as Helios, Jove, and Proteus.  With such a wide variety, it is impossible to generalize about the New Olympians.
New Olympian life-spans range between 13 and 250 years, depending upon the natural life-span of the mortal side of a New Olympian's ancestry.  They are almost all compatible enough to breed with each other.  It is also possible for some New Olympians to successfully mate with humans. 
The New Olympians are technically very advanced. Their island is protected by a cloaking device, and they have developed aircars (modeled after ancient Greek triremes in appearance), electricity, force fields, and even robotics (as Talos is evidence of). They are, in fact, ahead of humans technologically, although humans are quickly overtaking them.
The New Olympus government is currently a representative democracy, which meets at the Senate-House.  It was originally founded as a kingdom (and still referred to as such), but it is unknown when the island changed forms of government.  Some form of aristocracy exists on New Olympus, of which Jove is a member. 
A gargoyle clan lives on New Olympus, and has been given citizenship; the New Olympian Clan enjoy the same rights and duties as more "conventional" New Olympians. Their precise role in New Olympian society is as yet unknown, however they seem to be very isolationist, even by New Olympian standards.