Gargoyles (Folklore)

Gargoyles are stone creatures that line the roofs, gutters, and overhangs of various structures (often of the Gothic architectural style). At day, they remain inanimate atop of cathedrals, castles, overlooking the area below for any potential trouble (as well as diverting waterflow away from the building to preserve it), but at night, it is believed that the creatures animate, as evil spirits that may invade their (and even their inhabitants') homes.

Origin
According to legend, around 600 A.D. St Romanus of Rouen slayed or subdued a dragon-like creature by the name La Gargouille, which had been terrorizing the town of Rouen for centuries. Following Romanus's success, the townspeople burned the monster at the stake, however its head would not combust. The people then decided that instead, they would preserve the creatures head and mount it to the exterior of their church, which has since acted as a ward to fend off other dragons and evil spirits from attacking the town.

Description
Gargoyles are often made of stone, and are located atop various gothic structures (mainly churches and castles). Their features vary in appearance, ranging from having the appearance of various animals, such as goats or birds, but occassionally will have humanoid features as well. Some gargoyles (though not all) are depicted as possessing wings, indictating that they are capable of flight.

A gargoyle usually does not need to eat to survive, although in pop culture, they may ocassionally consume pigeons.

A common belief is that Gargoyles are actully living beings that largely resemble statues, while others are depicted as being demonic vessels.

Gargoyles' main job is to protect the structure(s) they are positioned atop of as well as the structure's inhabitants by warding off evil spirits and monsters being various supernatural means (similar to Jack o' Lanterns during Halloween). On a more realistic take, some gargoyles also act as waterspouts made to divert water way from structures as a means to help preserve them from water damage.

Popular Culture
Heroic Gargoyles have made numorous appearances in various forms of media.

Among some of the most well-known fictional gargoyles include Victor, Hugo, & Laverne, a trio of gargoyles from Disney's The Hunchback of Notre Dame, who serve as voices of reason to the film's protagonist Quasimodo.

Another well-known example are the titular protagonists of Disney's Gargoyles, who are led by Goliath; like their traditional counterparts, the team fights off evil monsters to protect humanity.

Outside of Disney, Constable Downspout from the Ankh-Morpork City Watch, who like most gargoyles of folklore, can remain completely still for entire days as a means to watch over the city he protects.

Trivia

 * In real-life, the actual name for a decorative gargoyle is "Grotesque", an actual gargoyle is a grotesque that is designed to have an open mouth as a makeshift water spout to drain water away from the structures they are constructed on, as a means to preserve them.
 * Although Gargoyles lining the rooftops of castles and cathedrals date back to the Dark Ages, the iconic Gargoyles atop the famous Notre Dame Cathedral in France where only added in the mid-1800s during a major restoration project.
 * A gargoyle resembling Darth Vader from Star Wars ines the north wall of the Wastington National Cathdral in Washington D.C., while one of the twelve gargoyles lining the Paisley Abbey in Scotland resembles the xenomorph from Alien.