They are "exiles from myth and legend, the outcasts of the gods and demons of every land bordering the sea. Defeated giants, fallen gods, dark reflections of beings of light. They are many races and none, joined together beneath the banner of the Fomor in a common cause." Their common cause is revenge.
By the appearance in Aftermath, Fomor are humanoid, of medium height, with sallow skin, greasy black hair, and an extremely wide mouth. They have dark, watery, bulging eyes, small sunken noses, long scrawny limbs, and very, very wide hands. They also have flaps of skin on their neck that they breathe air from. They look like a vicious frog, earning them the sobriquet "Frog Men".
It is stated that their abilities include sorcery, shapeshifting and clairvoyance. They practice entropy magic, and are not hampered by running water like most magic users. They give off a heavy anti-technology field. They are weakened by iron, as they used to interbreed with the faerie "before the Sidhe Wars."
They rarely deal with humans and appear to be ruthless and everyhere. They have been known to trade their handiwork for favors and influence. For some reason, the Fomor are especially prone to giving long winded, gloating, self praising monologues. They are probably the creators of the beasts used by the Denarians.
They are signatories of the Unseelie Accords. They are related to Jotuns. It is unclear if there is a distinct leader of the Fomor, though both King Corb, whose court is located in Lake Michigan, and the Empress seem to be possible rulers.
The Fomor easily have the resources to withstand the severely downsized Wardens, who have lost many of their best from the war with the Red Court. They have successfully kidnapped and murdered many of the less talented practitioners, who are now relying on the Paranet to stay safe, and the Wardens are too short handed to do much about this. The Fomor have prominent positions in most large cities in the USA and Europe as we are told in Aftermath and Even Hand. Although we are told in Cold Days that Carlos Ramirez was severely injured and Wild Bill Meyers has been "giving them Hell". They, however, do not have the resources to remove the Brighter Future Society, also called the Chicago Alliance.
Bob told Harry Dresden and Waldo Butters that before the time of the Sidhe Wars, there were all kinds of stories about the Fomor, the Daoine Sidhe, the Tuatha Dé Danann, the Tylwyth Teg, and the Shen — alliances, betrayals, battles and weddings were on an epic scale.
Push for power
In Aftermath, within hours of the fall of the Red Court, groups like the Fomor began to try to seize power and engage in genocidal tactics similar to those employed by Vittorio Malvora; only the Fomor do not kill, they twist and enslave.
In Ghost Story, their advances into the states and cities bordering large bodies of water have been the motivation for Baron John Marcone forming the Chicago Alliance between the Paranet, the Alphas, the Brighter Future Society, the outfit, the Einherjaren, and local White Court nobles. Their goal is revenge and therefore they seek power as their means—made easier to garner by the demise of the Red Court.
As of Cold Days, the Fomor have a strong foothold in Los Angeles, Seattle, Miami, and Boston. The White Council is fighting them mainly in Europe, and are at a stalemate. In the USA the Wardens in Baltimore, San Diego, and especially Wild Bill Neyers in Texas are fighting them off. In Chicago, Karrin Murphy, Lara Raith and Gentleman Marcone and their people together have also pushed them out.
In the series
In "Even Hand", Justine is sent by Lara Raith to deliver documents to King Corb under the protection of their courier. After departing, Cantrev Lord Mag of the Fomor drove away the courier and abducted her. As part of her mission from Lara, Justine stole account numbers, security passwords, and other records from Mag while freeing prisoners from Mag's home in order to cover up the theft.
Justine sought protection from Mag's pursuit from Freeholding Lord John Marcone, who granted it in order to protect the child she brought with her when she escaped. Once Mag arrived in force to take Justine back, Marcone killed him, and sent his body back to King Corb along with a weregild[Footnote 2] of approximately $250,000 in bullion. In exchange for the protection, he relieves Justine of the Fomor's account information.
In Aftermath, Fomor are kidnapping low-to-mid talented practitioners and causing nightmares in many magical beings. The disappearance of Georgia and Andi Macklin prompts William Borden and Karrin Murphy to investigate. Setting up a trap, they manage to track the two Alphas to a warehouse where they discover that the victims will sooner or later be converted into servitors. Engaging in battle, Murphy and Borden manage to bust the operation.
In Ghost Story, at the Chicago Alliance meeting, Abby reports that they have lost contact with Paranetters in Oregon. The group fears that the Fomor are responsible. Murphy tells Harry Dresden's ghost that the fall of the Red Court left a power vacuum and that the alliance has been pushing back incursions by the Fomor ever since.
Butters and Bob tell Dresden's ghost that the Fomor and Faeries are related and that both are repulsed by iron. Butters elaborates on the Fomor incursion and tells Dresden that though he is worried about her sanity, Molly Carpenter has made the difference between life and death in at least two battles against the Formor. He also explains that the Chicago Alliance Headquarters has become a safe place for the Paranetters, particularly to keep their children safe from the Fomor. Murphy informs Dresden that the Fomor have been using the magically talented (some approaching Warlock status) as officers and commanders.
Carpenter fights a pack of Fomor servitor as part of the Leanansidhe's combat training, while Dresden watches. Afterward, she talks with him about what the Fomor and their Servitors have been doing; how they hurt and kidnap people, including children.
One of the Fomor messengers, Listen, approaches the Grey Ghost's hideout from the side of the Nevernever. After being granted entry, they discuss the bargain between the Grey Ghost and the Cantrev Lord Omogh to turn the former into an ally able to face the Wardens. The Grey Ghost realizes that the servitors give very little thought to serf-preservation, except as a way to ensure maximum benefit to their masters.
Lea tells Dresden that the Fomor are dangerous folk to make bargains with. They were once the enemies of the Sidhe and were banished to the sea. She calls them outcasts of gods and demons, defeated giants and fallen gods. The Fomor are many races joined under the one banner in the cause of revenge
In Bombshells, a party is thrown to celebrate the signing of a non-aggression pact between the Fomor and Svartalves. Molly Carpenter describes the Fomor as "kind of an all-star team of bad guys", survivors and outcasts of mythology banded together under a single banner, who had been laying quiet for thousands of years. One of the Fomor Lords, the brother of Cantrev Lord Mag and named "Lord Froggy" by Carpenter, is found in a room inside the Svartalves' stronghold. He is described as tall, with out of proportion body parts and a very round stomach, looking very much like a gangling, poisonous frog. Lord Froggy and Listen plot to use a Fomor-magic bomb to attack the Svartalves guests, against the wishes of The Empress. He also remarks that the bomb he designed for the Red Court in the Congo was "deadly enough". Carpenter recalls a nerve gas which was used on a hospital tending wounded wizards. The weapon had killed tens of thousands of people in a city far smaller and less crowded than Chicago. When his deception is revealed, Froggy is dealt with by Etri. Listen survives the fight and walks out under his own power. 
In Cold Days, Thomas Raith tells Harry Dresden that the Brighter Future Society was founded by John Marcone and Lara Raith in order to repel the Fomor from Chicago. When Dresden expresses disbelief that they are bad enough to cause Raith and Marcone to work together, Thomas explains that the Fomor are ruthless, everywhere and carrying off anybody with magical talent. He explains that the situation is worse in Los Angeles, Seattle, San Francisco, Miami and Boston. They have not gotten a solid foothold in Chicago because of the work of Karrin Murphy, Marcone, Lara Raith and their supporters. Thousands of people have been taken and the White Council are too busy to help, apparently fighting the Fomor in Europe, particularly the Mediterranean.
In Skin Game, Fomor servitors disguised as caterers attack Harry Dresden, Hannah Ascher and Anna Valmont at a ball. They are after Valmont as she stole some data from the Fomor at the behest of Nicodemus Archleone. As they leave the ball, Dresden instructs one of the servitors to tell his master to leave town now that Dresden is back.
John Marcone has been fighting the Fomor since Dresden and Molly Carpenter have been absent, focusing mainly on areas where his territory is being threatened. According to Karrin Murphy, the Fomor have started taking children off the streets during Halloween.
In Peace Talks, the Fomor have convened a supernatural peace summit in Chicago, which John Marcone will host. While the intent is ostensibly to resolve current hostilities, the real intent is to allow their Empress, the Goddess Ethniu, to deliver an ultimatum to the assembled Accorded nations: abandon the mortals or die. The Fomor kill all of Baron Marcone's mortal caterers and guards as they enter purely to make a point, throw Gwynn ap Nudd's severed head into the peace summit to show their contempt for the Accords, and throw Mab through several walls of concrete to show their contempt for her. Ethniu then destroys the Chicago power grid, and the Fomor briefly retreat, pending an all-out assault on the city of Chicago. Worse, they are allied with the Outsiders.
Basis in mythology
Fomor (or "Fomorians") are a race of sea-based gods in Celtic lore. They are hypothesised to have been in Ireland before Partholon's invasion of Ireland, and engaged in long wars with the newcomers - Partholon's army, followed by his decendents the Nemedians, then the Fir Bolg, and lastly the Tuatha de Danaan. They are generally considered to represent the older native gods of Ireland, similar to the Greek Titans or Norse Jotunn. They are constantly defeated, in myth, but are never entirely vanquished; they're the equivalent of Celtic cockroaches. If cockroaches were amphibian magical badasses.[Footnote 1]
Arguably the most well-known Fomor of myth is Bres, the half-Fomor half-Tuatha who was given the role as the first High King of Ireland, in the hopes of finally uniting the two warring races. He turned out to be a tyrant who favored his Fomorian side, and was overthrown after a seven-year reign. His later defeat and death by Lugh forced the remaining Fomor to give up, and they allegedly returned to the sea.[Footnote 1]
- Skin Game, ch. 10
- Cold Days, ch. 19
- Ghost Story, ch. 23
- "Even Hand"
- Ghost Story, ch. 17
- Ghost Story, ch. 16 and 18
- Ghost Story, ch. 22
- Ghost Story, ch. 33
- Ghost Story, ch. 9 and 10
- Ghost Story, ch. 9
- Ghost Story, ch. 10
- Ghost Story, ch. 18
- Ghost Story, ch. 29
- Cold Days, ch. 17
- Cold Days, ch. 22
- Skin Game, ch. 11
- Skin Game, ch. 12
- Skin Game, ch. 24
- Peace Talks, ch. 1
- Peace Talks, ch. 28-29
- Peace Talks, ch. 30
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- Ireland’s First Mythical Inhabitants: The Fomorians | Faerie Lore
- The Fomorians - Irish Mythology Wiki
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