"There's a reason Link always dresses in green."
Celtic mythology is slightly different to its Greek, Norse, and Egyptian counterparts. Although there are deities in the Celtic pantheon, the folktales passed down through the ages are more concerned with heroes and heroines than gods and monsters. Consider the Arthurian canon, or the tales of Ireland's legendary Cú Chulainn: these are not ordinary almighties, but rather extraordinary human beings.
The Legend of Zelda has traditionally concerned itself with a similar kind of storytelling. Although many iterations of our green-garbed, not-so-eponymous hero exist, Link is often just a young boy tasked with defeating the nefarious Ganon. However, Zelda and Celtic mythology aren't just structurally similar.
Some of you may already know that Epona, Link's illustrious steed, is named after the Celtic goddess of fertility and protector of horses. Interestingly, after the Gauls fell under Imperial Rule, Epona was the only Celtic deity incorporated into the Roman pantheon.
The etymology of Epona is intriguing, as it builds on why this is such a fitting name for the horse we've all grown to love. In Gaulish, Epona meant 'Great Mare,' and was derived from the Proto-Indo-European (PIE) root word 'ekwos', meaning 'horse'.
When PIE was adopted by the Celtic Gauls and the Britons, the 'kw' sound from 'ekwos' slowly transformed into a 'p', particularly in Wales. So in Welsh, you now have 'epos' instead of 'ekwos.' We're halfway to Epona.
Theonyms, which are a branch of proper nouns reserved for deities, take on the suffix '-on'. So 'epos' becomes 'epon', and because Epona is a goddess, the name takes the Gaulish feminine singular, '-a', giving us Epona.
This etymological breakdown of how Epona's name came about forms a sound introduction to the relationship between Celtic mythology and Zelda. However, there are many more similarities. For example. Zelda's world is inhabited by a diverse cast of fairy folk. In his book Irish Fairy and Folk Tales, Irish poet W.B. Yeats separates the fairies of Irish mythology into two distinct types: trooping fairies, who live in groups and are benevolent towards their human cohabitants, and solitary fairies, who are often mischievous tricksters.
In the first case - trooping fairies - we can consider the Minish. Interestingly, the English translation of Minish Cap is the only version that has two different words for these thumb-sized mouse people: Picori, which is how the Minish refer to themselves, and Minish, which is how they're known to Hylians. This is likely a reference to the fact that there are multiple types of fairies, even within individual groups. It's like what Yeats discusses in his exploration of the fairy folk: we might have one name for them, but that's not all-encompassing.
It's also intriguing that Rem's shoe-shop in Minish Cap is most immediately comparable to The Elves and the Shoemaker, whereas The Brothers Grimm likely drew inspiration from the much older Irish tales of the unfortunately stereotypical shoemaking leprechauns and their drunken counterparts, the clúrachán. These are both types of solitary fairy, but the Minish have both trooping and solitary characteristics. On one hand you've got the eccentric Town Minish, whereas on the other you've got the sparse Mountain Minish society at Mount Crenet.
One interesting detail to point out is the relationship between contact with the Minish in Zelda and contact with the fairy folk in Irish myth. In the case of the former, a doorway between the Minish world and Hyrule opens outside Hyrule Castle once every hundred years. Similarly, the latter features tales concerning Samhain and Bealtaine, festivals during which a pathway to another realm is more likely to open. These liminal passages to alternate realms resemble routes to what's known as the Otherworld in Celtic mythology - but that's something I'll get to later.
The Minish are great, but the most intriguing fairies in all of Zelda are Skull Kids. Many solitary fairies from folklore are associated with child abduction, during which they replace a newborn or toddler with a fairy known as a Changeling. When Navi first encounters Skull Kid in Ocarina of Time's Lost Woods, she says, "Skull Kid - Is this what happens to kids who wander into the forest? It looks like he doesn't like grownups." Sure enough, if Link returns to the Lost Woods as an adult, Skull Kid will shoot needles at him using the flute Link taught him Saria's Song on earlier in the game.
In Majora's Mask, Skull Kid is ousted from Termina because the Terminians and Four Giants become sick of his mischief. Similar things occur no matter where solitary fairies appear - for example, consider godlings in The Witcher 3. These fairies like causing mischief with children, but are a nuisance to adults. Interestingly, the Skull Kid in Majora's Mask is implied to be the one from the Lost Woods in Ocarina of Time, as he tells Link, "Eh-hee-hee... You have the same smell as the fairy kid who taught me that song in the woods."
By the time we reach Twilight Princess, Skull Kid has become a whole new level of prankster. While he's guiding Link to the Master Sword, he forces him to play a game of hide-and-seek. After finding him several times, he finally escorts Link to the sword, but upon Link's return later in the game becomes hostile. At this point, Skull Kid plays Saria's Song on the way to the Temple of Time, implying that this is once again the very same trickster from the Lost Woods.
On top of Epona's etymological origins and the various types of fairy in Zelda, the inhabitants of Hyrule are ripped straight out of Celtic mythology. For context: Hylians are a race of people imbued with magic who resided in the skies alongside the goddess Hylia after their homeland - the Surface, now Hyrule - was ravaged by forces of evil. They named their new home Skyhold and gradually lost their magical abilities over the course of several millennia before (somewhat) safely returning.
If you refer to a poem from the Lebor Gabála Érenn - the Irish equivalent of Norse mythology's Prose Edda and Poetic Edda - you'll come across the following passage about the Tuatha Dé Danann, an ancient race of immortal magic-wielders who share a strikingly similar history with Zelda's Hylians:
"It is God who suffered them, though He restrained them
they landed with horror, with lofty deed,
in their cloud of mighty combat of spectres,
upon a mountain of Conmaicne of Connacht.
Without distinction to descerning (sic) Ireland,
Without ships, a ruthless course
the truth was not known beneath the sky of stars,
whether they were of heaven or of earth."
According to folklore, the Tuatha Dé Danann waged perpetual war against the evil Fomorians, who were nefarious, demonic creatures. In Whitley Stokes' The Training of Cú Chulainn, a Fomorian raider is described as having a "long, sinewy, hideous arm" while being "devilish" in stature. The supposedly monstrous Fomorians are therefore comparable to the monsters that flock to Ganon in the Zelda series, particularly Boboklins who match their description and similarly reside underground and in caves.
Cadence of Hyrule, the most recent iteration of Zelda, features a weapon called Caladbolg, which is named after the sword Fergus Mac Roich wields in an Irish tale from the Ulster Cycle (interestingly, a sword of this name also appears in Final Fantasy). However, the Master Sword itself is unsubtly derived from Celtic mythology. The idea of the Sword in the Stone is taken directly from King Arthur, when the eponymous hero accomplishes Merlin's task despite being only a boy. This sword is later replaced with the legendary Excalibur.
There's also another Master Sword equivalent in Irish mythology: Claoimh Solais, or The Sword of Light. This is often likened to Cú Chulainn's sword, known as Cruadín Catuchenn, and is one of Ireland's legendary god-killing weapons. Usually heroes need to complete three tasks before attaining the Sword of Light, or in some cases an equally powerful spear (see Lugh). These weapons are used to defeat enemies that are otherwise unkillable, which resembles the way in which the Master Sword must be used in order to defeat ultimate adversaries such as Ganondorf and Vaati. Interestingly, the Goddess' Harp - particularly the Skyward Sword variant - is strikingly similar to Dagda's harp, which is called Daur da Bláo, or The Oak of Two Blossoms. And while we're on the topic of music, let's not forget about the slip-jig from Wind Waker.
All of the above clearly likens the world of Zelda to the tales of Celtic mythology. However, there's another major similarity that transcends all the others. In Irish mythology, the Tuatha Dé Danann retreat to a place called the Otherworld after being uprooted from their home a second time, this time by our own ancestors.
In Celtic mythology at large, several Otherworlds exist. In Welsh folktales, one might encounter Annwn, whereas King Arthur's Excalibur was forged in the land of Avalon. Irish mythology features a range of Otherworlds, the most prominent of which is Tír na nÓg, meaning "Land of the Young". However, the most important Otherworld to consider in relation to Zelda is a lesser known Irish variant: Tech Duinn, which is an Old Irish term meaning "House of the Dark One".
Zelda has its own range of Otherworlds. Consider Termina in Majora's Mask, or the Twilight Realm from Twilight Princess. Generally, these are parallel dimensions existing as alternate versions of Hyrule. However, their existence, coupled with the ways in which Zelda evidently draws from Celtic mythology, gives us insight into one of the most complicated aspects of the entire Zelda series: its timeline.
At present, the Zelda saga is comprised of three alternate timelines that exist in parallel with one another. These lateral worlds all feature a different iteration of what's ultimately the same hero, which is quite confusing. However, they can be united by the Otherworldly whole the Celts believed in: Tech Duinn in Irish mythology, and Orbis alius in Gaulish.
This particular Otherworld is the one heroes ventured to after falling in battle. In her book Hy Brasil: The Metamorphosis of an Island, Barbara Freitag writes: "It was believed that the souls of the dead travelled to Tech Duinn; perhaps to remain there forever, or perhaps before reaching their final destination in the Otherworld, or before being reincarnated." The principles of Orbis are similar.
This is where Epona comes back into play. You see, the reason I went to such lengths earlier on to describe why the relationship between Epona's name and Celtic mythology is so meticulously interwoven is because traditionally, Epona is a psychopomp - a guide to the afterlife.
Because Epona exists in each timeline, it could be the case that Link's equestrian companion is the primary reason he can exist in all of them. Epona is the guide to the afterlife - in this case the Otherworld - and because so many Otherworlds appear in Zelda, it's highly likely that a Tech Duinn equivalent exists among them. This idea is particularly prominent in Breath of the Wild, where one of Link's titles is "The Hero who Sacrificed Himself for the Princess", while another is "The Hero Awoken from a Long Slumber". It's not farfetched to attribute this to a sacrifice in one realm and a reincarnation in another.
The Zelda series is teeming with references to Celtic mythology, to the extent that viewing it through the lens of Celtic legends could be the answer to understanding some of its most complex intricacies. That's not to say it's entirely based on Celtic mythology - there are instances of Greek, Norse, Egyptian, and Shinto influences sporadically dotted throughout the series too, as well as a plethora of references to other religions and myths. However, Celtic mythology seems to be the key to unravelling the mysteries at the heart of The Legend of Zelda. There's a lot more to it than Epona's name.