The Archfey are the god-like rulers of the fey creatures of Dungeons & Dragons, as you have probably surmised due to their sharing a naming system with the Archangels, Archdevils and Archomentals. Of all their kin, the Archfey are the least detailed and most forgotten, which is understandable given that D&D couldn't even decide if faeries were or weren't extraplanar beings until 4th edition.
Great Wheel Archfey
In the Great Wheel, the archfey were first introduced as the Seelie Court, a cluster of deities united by their shared patronage of various fey races. They inhabited a wandering demiplane that shifts between the Upper Planes as it sees fit, mostly wandering between the Beastlands, Ysgard and Arborea. In comparison, the Unseelie Court was located in Pandemonium, where it served as the underlings of the outcast fey goddess known as the Queen of Air and Darkness. Then 5e rolled around, and all the Fae got lumped together into a single inner plane called the Feywild, which filled roughly the same cosmological niche as the Positive Energy Plane did in prior editions (emphasis on "roughly", since the Positive Energy Plane is still around, it's just been moved to "outside" of the Great Wheel rather than being part of the Inner Planes).
These gods first appeared in the 1992 sourcebook "Monster Mythology", which looked at the gods of the various non-human races. They would receive some minor expansion in 1996's "On Hallowed Ground", in the form of a clear-cut table denoting their areas of concern, holy symbols, and places of residence in the cosmological setting of Planescape.
The archfey of the Great Wheel faded into obscurity with the coming of 3rd edition. Most notably, the Plane of Faerie was presented as an optional co-terminous Outer Plane (Mildly Neutral Aligned, Enhanced Magic, Flowing Time (1 day Faerie = 1 week Prime), Light Gravity, Infinite Size, Alterable Morphic, No Elemental or Energy Traits) in the 3e Manual of the Planes, with the Seelie & Unseelie Fey being presented as fey creatures with the Celestial or Fiendish template respectively. Skerrit would receive an update to a 3e patron god in "Complete Divine", whilst The Queen of Air and Darkness would reappear only in brief as one of the Forgotten Faiths in the back of Dragon Magazine #359.
The Planewalker fansite for Planescape created its own, modified version of the Faerie Pantheon as part of its unofficial 3e update, most notably portraying Titania and the Queen of Air & Darkness as different sides of the same fey deity, Queen Mab.
Non-godly portrayals of Oberon, Titania and "Puck", an analogue to Squelaiche, appeared in Dragon Magazine #263, whilst an alternative "Fairy Queen" goddess named Rhiannon is presented in Dragon Magazine #155.
Titania is the Queen of All Faeries, a goddess whose portfolio consists of faeries, the kingdoms of faeries, friendship and magic. She is described in Monster Mythology as a beautiful female faerie, only three and a half feet in height, with gossamer wings, pale skin, a perfect complexion and cheek bone structure, and penetrating blue eyes, carrying a diamond-tipped wand. Sister to the Queen of Air & Darkness, she is also believed to be somehow connected to Cegilune, the malign moon goddess who serves as the patron goddess of hags. Her symbol is a white diamond with a blue star glowing in its center. Whilst all non-evil fairies respect her, worship of Titania is most prominent amongst the brownies, pixies and sprites.
Oberon is Titania's prince consort, a fey god of nature, wild places, and animals who spends most of his time roaming Arborea and the Beastlands, hunting wild beasts for his entertainment. His holy symbol is a white stag, and he appears as a male fairy of perhaps unusual size (4' 6") with no wings, and strongly muscled by fey standards. He is known to be allied with Corellon Larethian and Sehanine Moonbow. Unlike his wife, no particular fey race is especially close to his heart, though all seelie fey love and respect him.
The Queen of Air and Darkness is said to be Titania's corrupted evil sister, a malign fey deity whose portfolio covers magic, illusion, darkness and murder. Normally invisible, this cold and emotionless creature, whose true name has been forgotten for ages, can be perceived magically as a faerie with pale, angular features, blood-black eyes, and a mane of black hair. She is beautiful, but hers is a terrible, eldritch beauty that chills the bone. Her unholy symbol is a black diamond. Because she embodies the corruption that can take root in the heart of the elvish race, many members of the Seldarine - Corellon Larethian, Erevan Ilesere, Rillifane Rallathil, Sehanine Moonbow, and Solonor Thelandira - all despise her, and consider her to be as much an enemy as Lolth. In 3rd edition, she grants access to the Cleric Domains of Air, Chaos, Darkness and Trickery, and her portfolio is given as being darkness, magic, murder and evil fey.
Verenestra is one of Oberon & Titania's children, and is the fey goddess of female faeries, charm and beauty, whose holy symbol is a filigree-edged silver mirror. Needless to say, her worship is most popular amongst dryads, nymphs and sylphs.
Damh is Verenestra's brother, and the only other member of Oberon & Titania's family to sit amongst the archfey of the Great Wheel. In appearance, he resembles a korred or a satyr; a humanoid fairy with the cloven-hooved, digitigrade legs of a goat and long, tawny-auburn hair tied into braids. Fey god of dance, song, and celebrations, his holy symbol depicts flutes, pipes, drums and harps, all instruments that he himself plays. In addition to being the patron of all fey bards, he is the racial patron of the korreds, satyrs and the atomies - the tiniest breed of sprites.
Squelaiche is the fey god of leprechauns, trickery and illusions, and is basically a masterful leprechaun illusionist who serves as the Seelie Court Jester. He uses both a clover leaf and a red pointed hat as his holy symbols.
Eachthighern, who may have the worst name of the entire mock-Irish/Celtic faerie pantheon, is the god of unicorns, pegasi, healing, loyalty and protection. Appearing as a majestic winged unicorn, with a unicorn's horn as his holy symbol, Eachthighern is known for serving as the steed of Oberon.
Emmantiensien is the god of treants, trees, and the magical energy that rises from deep, hidden places. His worshippers use a dual-acorn symbol to show their faith, and he appears as a massive treant with well-sheened bark and a mysterious magical crystal clutched in his roots. He known to be closely allied with Rillifane Rallathil and Corellon Larethian.
Nathair Sgiathach is the fey god of mischief and pranks, which you might suspect to be a rather redundant position. He appears as a Faerie Dragon, and may in fact be the same deity as Hlal, just in a different identity. Whilst he is considered the racial god of faerie dragons, he is also popular amongst pseudodragons, sprites, pixies and grigs.
Skerrit is the racial god of centaurs, although he is also considered the fey god of forests and those who would live in harmony with them, as his title of "The Forester" and his holy symbol (an oak sprouting from an acorn) would suggest. He is the least-connected to the archfey pantheon, but simultaneously the most well-known- he had his own appearance in the Planescape supplement "Warriors of Heaven", which was all about playing angel and aasimar PCs, whilst in 3e he was promoted to full god status in the official splatbook "Complete Divine", as well as appearing in its 3.0 precursor "Defenders of the Faith". Aside from centaurs, he's also popular with satyrs and with sylvan elves.
World Axis Archfey
When 4th edition came out, one of its design statements, declared as early as "Worlds and Monsters", was this: Make the Fey Interesting. Thus, the Feywild came to be, and the Archfey were given a complete makeover.
First appearing in the 4e version of the Manual of the Planes, the archfey are described as the godlike rulers of the Feywild, beings that originated from its innate magic and ascended to rule over it, strengthening the fey's nature as being as much powerful extraplanar beings as angels, fiends or elementals. The Archfey themselves are an eclectic array of beings, ranging from elemental-like spirits of natural phenomena to ascended eladrin to elder fey beasts to extraordinarily powerful individuals of the various fey races. This eclectic group meets at random intervals to form the Court of Stars, which is sort of like the United Nations of the Feywild. They further organize themselves into various factions based on certain shared themes.
The Summer Fey represents the largest and most powerful faction within the Court of Stars, namely as its leader, Tiandra, the Summer Queen, is without question one of the mightiest of all archfey. She also happens to look with the most favor upon mortal races, which is a good thing.
The Green Fey faction covers those fey most associated with the wilderness. Its current leader is Oran, the Green Lord, Tiandra's tempestuous on-again, off-again lover.
The Winter Fey are from the icy lands to the north of the Feywild, and have a reputation as one of the more sinister and dangerous factions to mortals. Its unofficial leader is the Prince of Frost, once the son of Tiandra and known as the Spring Prince until the fey maiden he loved broke his heart by choosing a mortal man over himself.
The Sea Lords are those fey who are tied to the waters of the Feywild, such as merfolk and nixies. Their current leaders, the youngest of the faction leaders within the Court of Stars, are former-eladrin twins called Elias, who takes charge of the shallow waters, and his sister Siobhan, who takes charge of the deep waters. This faction is also referred to as the Court of Coral in Heroes of the Feywild.
The Gloaming Fey are more abstract in nature than the Green Fey or the Sea Lords, and are associated with things such as dreams, darkness, stars, twilight, dusk and other nocturnal phenomena. The most loosely organized of the factions, they are also the most secretive. Archfey associated with this faction include the Maiden of the Moon, who does endless battle against nightmares, werewolves and therianthropes; the Prince of Hearts, a meddler who seeks to manipulate the loves of mortals for his own amusements, and the dread prophet known only as the Witch of Fates.
The Unseelie Court is only mentioned in passing in the sourcebook "Heroes of the Feywild". It is described as less a faction and more a general term for fey creatures associated with evil, maliciousness or corruption.
Dragon #374 covers The Prince of Frost, mightiest of the Winter Fey, extensively detailing his origins and even providing details on how to use him as a patron for a fey pact Warlock, complete with Paragon Path in the Long Night Scion.
Dragon #376 mentions the names of several archfey associated with the island of Sarifal in the 4e Forgotten Realms, but only their names: Relkath of the Infinite Branches, Lurue the Unicorn Queen, Verenestra the Oak Princess, Sarula Iliene the Nixie Queen, and Aurilandür the Frost Sprite Queen. It also mentions Deep Sashelas, a member of the Seldarine associated with merfolk and aquatic elves in the Great Wheel.
Dragon #420 covers The Carrion King, patron lord of the Myconids of the Feydark. A strange thing even by fey standards, the Carrion King's mind is many-splintered, scattered in different individual personalities and memory traits across his many bodies, which all flow through the Feydark. However, he is one of the most friendly of all archfey, and welcomes adventurers with open arms - unless they try to destroy him.
Dragon #420 also covers Thrumbolg, First Lord of Mag Tureah, who is the mightiest and maddest of the dread fomorians, prophesied by Baba Yaga herself to be immortal until struck down by one of his sons - a prophecy that can only be fulfilled with the lost relic-blade known as Fragarach. Controlling Mag Tureah and its endless array of portals, Thrumbolg is one of the few fomorians that the archfey are forced to treat with on equal terms.
Dragon #422 covers Hyrsam, Prince of Satyrs, a wandering minstrel with a dark secret and mad dreams of anarchy. The son of Oran of the Green Court, he yearns to destroy civilization within the Feywild and revert it to primal wilderness.
Dragon #428 covers Cerunnos, the Horned Lord, an outcast firbolg adoptive son of Oran, cursed by the Prince of Frost and the Summer Queen both, so that now has nothing left but the leading of the Wild Hunt.
Dungeon #185 covers Selephra, the Bramble Queen, a fallen Green Court fey who may have once been a dryad or a proto-hag, but who is now a monstrous thing that yearns to make mortals suffer. She is also briefly mentioned in Dungeon #195's "Bestiary: Flowers in the Darkness", where it is said that she cultivates vampire roses.
Dungeon #205 covers Tuxil, The Trinket Lord, a mad gnome with the ability to assume the shape of a fox who has become lord of a strange place where all lost things end up.
In addition to the above, a number of other archfey are mentioned in passing. "Manual of the Planes" refers to Scamander, the Cat Lord and the Monkey King. "Dragon Magazine" and "Dungeon Magazine" mention several more.
Dragon #386 mentions The Rose King, an archfey who claimed to be the son of Corellon and who got killed leading a crusade against the Drow; his legacy, ironically, survives in the form of his half-drow daughter and the drow-fighting organization dedicated to him and Corellon that remains.
Dragon #393 features The Lady of the White Well, a cursed bastard daughter of Sehanine who is condemned to never leave the proximity of the pool where she was conceived until she gives her heart to a worthy lover, so she empowers hexblades who agree to quest and prove worthy of becoming her husband.
Dungeon #162 features the adventure "Winter of the Witch", where the party must battle a Winter Court archfey named Koliada, reputed to be the daughter or sister or lover (or more than one of those) of the Prince of Frost himself.
In Dungeon #166's "Throne of the Stone-Skinned King", the party must impress an airy archfey known as the Skyshaper to complete their quest.
In Dungeon #178, mention is made in "Backdrop: Chessenta" of Sebakar, a malevolent archfey of the Forgotten Realms concerned with crocodiles who was born of a union between the Mulhorandi god Set and a bestial archfey called Mornach.
Dungeon #178's article "Explore Taer Lian Doresh" presents a mad, malevolent archfey of Eberron called Shan Lian Doresh, Lord of the Fading Dream.
Dungeon #190 has the adventure "Force of Nature", in which the party must stop a mind-controlled archfey in the form of a bull elk so huge it can crush castles under its hooves.
Finally, Dungeon #217 has the adventure "A Rhyme Gone Wrong", where the party must defeat the machinations of a malevolent, dream-haunting archfey called Felsa, the Slumbering Queen, a would-be conqueror who escaped punishment by placing herself in an enchanted slumber.
Fufilling the same role as Archfey in Pathfinder are the Eldest. The Eldest are the most powerful of the fey that inhabit the First World (the god's first draft of the world with weird physics and infinite lives.) and are capable of granting spells. Since the First World is an entire plane and thus infinite, there are a lot of Eldest, but only a dozen have been named since most vistors never go that far beyond the equivalent of their home planet. Surprisingly, Eldest can be of any alignment, but no good Eldest have been revealed.
|The inhabitants of the Planes of Planescape|
|Upper Planes:||Aasimon - Angels - Animal Lords - Archons - Asuras - Eladrin - Guardinals - Lillend|
|Middle Planes:||Formians - Githzerai - Inevitables - Marut - Modrons - Rilmani - Slaadi|
|Lower Planes:|| Alu-Fiends - Baatezu - Bladelings - Cambions - Demodands - Erinyes - Hags |
Hordlings - Imps - Kytons - Marilith - Obyrith - Succubi - Tanar'ri - Yugoloth
|Transitive Planes:||Astral Dreadnought - Githyanki|
|Inner Planes:||Azers - Elementals - Genies - Grues - Mephit - Salamanders - Sylphs|
|Sigil:||Dabus - Cranium Rats|
|High-ups:||Archangels - Archdevils - Archfey - Archomentals - Demon Princes|