The Fae:
Aka fairies, fay, fair folk, faeries, fey. 

Roots in disparate European folklore: Celtic, Slavic, Germanic, French. 
Pagan deities, spirits of the dead, ‘demoted’ angels and demons, precursors to Mankind, or spirits of nature. 

Traditionally human-like with fair appearance, magical qualities, and a penchant for trickery. 
Can also refer to goblins, gnomes, sprites/pixies, ogres, trolls, and other such magic creatures rooted in above regional folklore. 

Recurring motifs are trickster behaviour and the use of protective charms to ward off fairy/fairy influence eg church bells, inside-out clothes, four-leaf clovers, gifts of food (most commonly bread), cold iron, etc. 

Fairies may stem from a root in Persian Mythology of the ‘Peris’, angelic beings said to be fair, beautiful, extravagant nature spirits, skilled in magic and supported by wings. 

Size is not a constant in fairy folklore and they may be diminutive, of average human height, or several feet taller depending on mythology. Height is not also constant to one individual fairy - it may be a magical construct or affectation, changed at will. 

Wings are common in Victorian and later era artwork, but are less prevalent in older folklore, where fairies are airborne under their own magic, or perched on ragwort stems, or on the backs of birds. 

Some folklore paints fairies as ancient pagan deities, such as nymphs, dryads, and tree spirits, who lost reverence and perceived power following the rise of the Christian Church, and so who’s magical power dwindled in kind. 

Celtic, particularly Irish, folklore favours fairies as the spirits of the dead; banshees, ghosts etc are of the fae, and the Irish ‘sídhe’, the etymological root for the Irish term for fairy, were burial mounds. It was deemed dangerous to eat the food left for the dead, and fairies were depicted as living underground where the corpses had been buried. 

Fairies are often depicted as pranksters - tangling hair (‘fairy-locks’), stealing small items, and luring travellers into becoming lost. However they exhibited more dangerous behaviour - sudden, unexpected deaths were attributed to abductions, with the corpse being a magical wooden replica. 
Charms and wards were necessary to protect oneself and one’s home from fairies; cold iron, amulets and talismans of rowan trees and/or various herbs, or rowan trees (considered to be sacred to fairies) growing in one’s garden. 
It was also advised to shun or avoid places “known” to belong to fairies, to avoid insulting or offending them. Avoiding insult in general was important to protecting oneself from fairies. 

In Scottish folklore, fairies are divided into the Seelie and Unseelie courts. While both engaged in trickery against humans, the Seelie Court was seen as more harmless pranksters and more likely to be more beneficiently inclined towards humans, while the Unseelie Court was more malicious, bringing intentional harm to humans for their own entertainments. Both courts however were equally dangerous if offended. 

A considerable amount of folklore around fairies deals with abduction, particularly changelings (the replacing of human infants with fairy imposters), although adult abduction is not uncommon. 

Avoiding fairy-occupied spaces, fairy-travelled paths, or digging into fairy land is heavily encouraged. Home owners would knock down corners that intruded on fairy paths, and cottages would be be built with aligned front and back doors, that could be left open to maintain a clear, un-obstructed fairy path. Fairy forts and fairy trees were left undisturbed, not even the grass being cut. 

It was important not to offend fairies; either by complaining about them, or by taking false credit for their work. Gifts deemed of poor quality would lead to insult, as would looking too long at a fairy (infringing on their privacy). 

It is believed that names have power over fairies, and that by knowing a fairy’s name, you could summon and command it. Doing so however would gravely insult the fairy. 

A common feature in fairy folklore is the use of magic to disguise objects or persons. Fairy gold would appear as solid coin, but eventually reveal itself to be enchanted pebbles or gorse blossoms or gingerbread cakes, or other similarly worthless items. 
Fairy ointment, applied to the eyes, allows one to see through these illusions; however, again, this poses a risk, as in some tales those who had applied ointment to their eyes and been discovered were then blinded. 

In Irish folklore, fairies are descended from the Tuatha Dé Danann, a race of supernaturally-gifted people and the gods and goddesses of pre-Christian Ireland, supposedly having their origins in the islands to the North, or from the sky. After victory in battle against other supernatural beings, but suffering defeat at the hands of the ancestors of the modern Irish people, they were said to retreat underground to the sídhe, living on as fairies.