Vaadin is a mythological creature in Finnish folklore, the goddess and divine ancestor of the mountain reindeer. It appears frequently in the poetic mythos, often as the trustworthy steed of either Seppo Ilmarinen or Väinämöinen, the two divine hero figures. In many of the stories, it is referred to as Steed of Seppo or Seponratsu in Finnish. An artifact itself, according to most accounts, Vaadin helped Seppo Ilmarinen in his quests to find the knowledge necessary to forge magical artefacts, such as Sampo.

Some of the Vaadin poems were collected by Elias Lönnrot, but he left them out of Kalevala, the Finnish epic poem, as they were somewhat detached from the main theme and would have created inconsistencies with the poems included in the epos. Lönnrot edited Kalevala heavily and it represents a selection from a much larger and more diverse body of collected poems. Many of the accounts regarding Vaadin were sung by shamans, and still are. A shamanistic tradition, centered on the tales of Seppo and Vaadin, still lives in South-Western Finland, around the city of Turku. Some research in the folklore suggests that the origin of Vaadin is as a shamanistic animal spirit used during trance for voyaging to Tuonela, the Land of Dead, with its mechanical construction reflecting the shamanistic tools used for guiding the trance. While the shamanistic interpretation of the origins is disputed by a majority of the research community in a maximalist sense, it is considered a potentially important component in the collection of traditions that preserve the folklore.

Origin or birth poems, synnyt in Finnish, provide the most distinct accounts of mythological artefacts in the Finnish folklore, as origin poems or songs were central in the traditional magical practices. Vaadin is no exception and its origin poems are numerous. In many of the versions, Vaadin was created in a mill, for which Seppo had built the millstone. After many a year, grinding the sacred acorns of the Great Oak (a version of the World Tree in Finnish mythology), the millstone had become saturated with the magical juices of the acorns. Seppo found that the stone could be used to make tools. He cut it in many pieces and built a toolkit suitable for fashioning spider web into any imaginable shape. When Seppo started making Sampo, he needed a steed that would help him find the precious components and the knowledge he required. The magical tools became the skeleton of Vaadin.

"Lost, his mind was,
gone, was his understanding,
ran away, were his memories,
in the vast land of hills of stone.
Make a steed he had to,
forge bone out of stone,
flesh out of moss,
and skin of bark of the birch.
The length of his hammer,
he put as the spine and the hip,
bellows as the lungs,
tongs as the legs, paired.
So woke Vaadin from the first slumber,
lichen did Seppo give her for eating,
mead did he give her for drinking,
then mounted her for the journey."

Other versions associate the creation with Väinämöinen instead of Seppo Ilmarinen, and give different accounts for the materials. This ambiguity can be largely explained through the frequent cooperation between Väinämöinen and Seppo in the mythos.

The Kalevala associates a perverted Vaadin-like creature with the evil antagonist Hiisi. The creature, Elk of Hiisi, is chased by Lemminkäinen, the third hero in Kalevala. While this is antithetical to the other accounts of Vaadin, it is noteworthy in how it blurs the distinction between the mountain reindeer and elk, and how it makes clear that the steed is an artificial construct.

But the boast was heard by Hiisi,
And by Juutas comprehended;
And an elk was formed by Hiisi,
And a reindeer formed by Juutas,
With a head of rotten timber,
Horns composed of willow-branches,
Feet of ropes the swamps which border,
Shins of sticks from out the marshes;
And his back was formed of fence-stakes,
Sinews formed of dryest grass-stalks,
Eyes of water-lily flowers,
Ears of leaves of water-lily,
And his hide was formed of pine-bark,
And his flesh of rotten timber.

(Translation by W. F. Kirby, 1907)

Nevertheless, proper names are rarely used, so the identity of the steed or steeds remains largely implicit in the myths and, because of the differences in the origin myths, can not be unambiquously associated with a unique identity.

The theme of animal ancestor gods is common in the Finnish myth, as we can see in the widespread worship of Tapio, the lord of the bear and the forest. With respect to Vaadin, the identification of the animal is not completely clear. The Finnish word vaadin refers specifically to an adult female of the semi-domesticated mountain reindeer, which lives in the Northern Finland in Lapland as well as in the Northern Sweden and Norway. On the other hand, the Finnish folklore represented in Kalevala and other collections has been collected from Southern Finland, where the mountain reindeer does not exist. Nevertheless, Southern Finnish folklore and Kalevala do include many other elements as well that are distinctively from Lapland, such as the hunting of the Elk of Hiisi, so we may assume that the folklore reflects a record of cultural interaction. The distinction between the northern mountain reindeer and the deer species of Southern Finland, the forest reindeer and the elk, is clear in the modern language, but may have been less clear in old Finnish dialects, as is reflected in the Kalevala account. Peura, reindeer, may have been a generic word for a wild animal, as can be seen in jalopeura, the old Finnish word for lion. Kalevala uses the poropeura in the Lemminkäinen story to distinguish the specific sub-type of reindeer. The identification is further complicated by the fact that other lines of poems included in Kalevala often refer to a horse in association with Seppo and Väinämöinen. To some extent, this could be due to the use of the word for horse as a generic name for a steed. While a mountain reindeer is not suitable for riding, animal gods are typically portrayed as uncommonly large in mythology, even to the extremes, so the identification fits quite well in the variety of magical mounts.

The mythology related to Vaadin, especially as represented in Kalevala, locates some important characters and people in Pohjola, a mythical land in the north from where all evil originates, according to most accounts. For example, Louhi or Pohjolan emäntä, Queen of Pohjola, is the primary antagonist in the Kalevala mythos. Both Seppo Ilmarinen and Väinämöinen make services to Louhi to earn the hand of her daughters for marriage. Vaadin is often mentioned in connection with these services, such as the making of Sampo. On the other hand, as Sampo can be identified with the mill mentioned in creation stories of Vaadin, its identification in the stories becomes unclear.

While beginning its life as an artifact, Vaadin is later represented as an antropomorphic divine being. This is in contrast with the Bride of Gold, another creation of Seppo, which failed to become a fully living and thinking being. Finding magical ways around fundamental problems in life are central in Kalevala. In some areas, magical solutions are morally acceptable, while in others they are not and the successes and failures in the mythos reflect this ethic. Research in the folklore regarding the Bride of Gold myth has provided support for a theory that creating a wife would go against very fundamental social rules of courting and mating, paralleling the disapproval of "playing god" in acts involving life and death (though "cheating death" is usually considered a positive act). The main motivation of the protagonists in Kalevala is courting young daughters, which always ends in failure, usually for similar reasons. Animals, such as Vaadin, are outside the social context and considered to belong in the same category with tools and machines. The Vaadin myths present a noteworthy example of this categorization of animals and tools in the same category at an archetypal level.

The Vaadin myths parallel the Sleipnir myths in the Scandinavian mythology. This connection is especially visible for the connection of Väinämöinen with Odin, who used Sleipnir in his journeys. The use of tongs for the legs of Vaadin actually suggests eight legs, which is the distinguishing attribute of Sleipnir. While Sleipnir is almost universally depicted as a horse, the exact identification of the steed may have changed during the transmission between the cultures.

The Bridle of Vaadin is a special artifact itself. There is no headstall, but only the rein, detached from the creature, kept in the hand of the rider. The rein is a chain or set of "gadgets" used for controlling the creature. The rein was built of web with special tools, with Seppo wearing magnifying goggles to work out the small details.

The significance and cultural influence of Vaadin can be seen in its identification with a constellation in the traditional Finnish constellation system. The famous French astronomer Pierre Charles Le Monnier (1715-99), who visited Lapland, introduced the constellation to international star charts with the name Tarandus vel Rangifer. The constellation was present in many star charts of the time, perhaps most notably in the Uranographia published in 1801 by Johann Elert Bode, as shown in Figure B.1, “Constellation of Tarandus vel Rangifer in Bode's Uranographia (1801)”. It was later removed in the unification of the constellation system towards the Greek mythology.