Gargoyles are nocturnal creatures that turn to stone during the day. They originate from the titular series of the same name, Gargoyles, which includes gargoyles as part of the main cast.
Gargoyles once lived in every corner of the world, living in elevated areas as their natural habitat and to protect their eggs. Gargoyles would spend their nights guarding the rookery and foraging for food; their days hibernating in the open air. When the Iron Age of Man arrived, the gargoyle's stone hibernation, which had once been a natural form of protection, became a liability. Men could safely seek out gargoyles during the day and use iron weapons to smash them to bits. Many gargoyles were destroyed, and the race nearly perished.
One factor saved them, however. People were more afraid of each other than of gargoyles. One very wise man struck a deal with a gargoyle. He would build his keep on top of a gargoyle rookery. During the day, his archers could keep both humans and sleeping gargoyles safe from enemies and harm. During the night, the gargoyles would do likewise. It worked out great, and the idea caught on like wildfire. Soon castles, keeps and fortresses were popping up atop every accessible rookery. Existing castles and new castles that could not find a rookery to co-exist with were carving fake gargoyles out of stone, to fool potential enemies into believing that their castle was also protected by gargoyles. This was the golden age of human-gargoyle relations. But it couldn't last.
Gargoyles are bipedal organisms belonging to the fictional order of animals gargates, and are generally more physically powerful than humans. They are related to gargoyle beasts, in the same way as humans are related to apes. Being nocturnal, gargoyles are very adept at concealing themselves within shadows, perfectly camouflaging themselves in the dark for ambushes, or simply to get around stealthily. In fact, apart from their inherent strength and beastly features, the cover of the night is generally a gargoyle's strongest weapon against their adversaries.
Gargoyles exhibit tremendous visual variety. For example, some have hair and some don't. Most gargoyles have crests on their foreheads in addition to horns, but some gargoyles lack one, the other, or sometimes even both. Some have relatively round, humanoid faces; some have more animalistic snouts. Most have prehensile tails, many have six limbs (not including their tail) with four digits per limb: usually two arms (each with three fingers and an opposable thumb), two legs (each with three forward toes and a back claw) and two wings (where the four digits are often divided between ribbing for the wings and/or finger-like grasping claws at the wings apex), though among Mayan gargoyles, it is not uncommon to have a snake tail instead of legs, and among the Japanese gargoyles, it doesn't appear uncommon for any to have feet with two forward toes instead of three.
Gargoyle eyes also glow to signify intensified behavior; male gargoyles' eyes glow white when in an excited stage, and females' eyes glow red, signaling an adrenal response.
All gargoyles are shown to have a pair of wings that vary in appearance and size. Most of the Gargoyles featured in the series have wings resembling a bat's while others such as the London Clan, and some of the Mayan Clan, have feathered wings, resembling a bird's. The rarest wing variation are those like Lexington's, stretching between his arms and legs, rather than extending from his back as with other Gargoyles, somewhat resembling a flying squirrel.
Contrary to popular belief, these wings are used for gliding and are incapable of powered flight. In order to accomplish this, the gargoyle will typically launch themselves from high perches or ledges, thus allowing them to achieve lift using currents of wind. They are quite prehensile, able to fold around their bodies in a cape-like manner. The bones in the wings seem to curve when they do this, which suggests that the main "arm" of the wing is not a single, solid bone, but a series of smaller, connected bones, somewhat resembling a spinal column. This, however, is unconfirmed.
Gargoyles turn to stone at sunrise and will remain as such until nightfall, at which point the surface layer will crack and flake away, revealing flesh and blood underneath. Gargoyles generally refer to this as "sleeping". During this period (daytime), the stone form is absolute, and they are effectively indistinguishable from regular statues.
While in stone form, all physiological functions of the Gargoyle in question are stopped, with the exception of the their natural recuperative processes, which seems to be even augmented in exchange for the other bodily attributes halted throughout the duration of stone sleep.
The stone form appears to be quite durable, given that the Wyvern Clan, managed to survive a thousand years in this state, without any apparent degradation. It is not, however, indestructible, as a human with a strong arm, and the right bludgeoning tool can shatter it. If the stone form is seriously damaged, then the gargoyle will die, without ever waking up.
The stone sleep is rejuvenating, and most of the gargoyle's injuries will heal by sunset. There do appear to be limits to this, however, as Hudson's eye never healed after the Archmage blinded it (although, this could just as easily be the result of the injury being magical in nature, or the effect lessening with old age).
All gargoyle offspring hatch from eggs, but female gargoyles will only lay a single egg on the following spring equinox. All of the eggs will be stored together in the clan's rookery, and the communal hatching occurs ten years later. The gargoyle offspring will typically inherit their body structure from the matching gender parent (mother to daughter, father to son), while their pigmentation will be derived from the other (father to daughter, mother to son).
While not inherently immortal, gargoyles can be extremely long-lived, a result of stone sleep which seemingly slows or halts their aging process to an absolute standstill until they wake again the following night. This was how the Manhattan Clan were able to survive all the way to the 20th Century, after Magus cast the spell where they won't awaken from stone form until "the castle rises above the clouds", being in stone sleep the whole time.
Even in old age (as evidenced in the episode Grief, and by Hudson throughout the series) they are not as frail and incapacitated as other creatures. Because they spend half their day asleep as stone, they age at half the rate of a human, thus living twice as long.
The gargoyle culture is defined primarily by their natural instinct to protect. They are guardians by nature and will continue to help and protect any humans within their "castle" or protectorate, even if those humans hate and fear them for many years. Only a few gargoyles have been known to stray from this path (Demona and Thailog for instance). Traditional gargoyles seem to believe that their brethren and human must work together for symbiotic coexistence; with humans protecting gargoyles during the day, and gargoyles protecting them during the night.
Members of the clan are not necessarily related biologically. Nevertheless, the gargoyles in a clan will consider themselves members of a single extended family, often referring to others of their generation as "Rookery Brothers" or "Rookery Sisters". This reflects the fact that gargoyles are hatched from eggs, which are stored communally in a rookery. As such, parents are never certain which of the hatchlings is their biological offspring. Rather, hatchlings are "children of the entire clan".