Fertility figures, who fought a war against the AEsir, and exchanged hostages. The god Njord was one of those who was given to the AEsir, and he and his two children, the gods Frey and Freya, although formally counted among the AEsir, maintained their affiliation with their former kin. The Vanir are also indirectly involved in the myth of the Mead of Poetry, since Kvasir, from whose blood the Mead was made, was himself first created from the shared spittle of AEsir and Vanir with which the truce was formally concluded. The longest account of the war between the Aesir and the Vanir is given by the 13th-century Icelander Snorri Sturluson in Ynglinga Saga:

Odin took his troops to battle against the Vanir, but they still became aware of it and defended their land so that neither side could win. Each to spoil the other's territory and did much damage; when they both grew weary of this, they agreed a peace meeting, naked truths and exchanged hostages. The Vanir offered their most distinguished men, Njord the Wealthy and his son Frey, but the AEsir took someone named Hoenir, whom they called a splendid chieftain: he was a large and handsome man. They sent Mimir with him, a very wise man, and the Vanir offered the cleverest of their number, who was called Kvasir.

The vanir are distinguished from the asir, the dominant group to which Odin and Thor and their consorts belong, but they are also subsumed within it, so that the word asir generally refers to both groups. The word vanir is related etymologically to the word for “friend” in the Scandinavian languages and to words in other languages meaning “pleasure” or “desire.” The vanir joined the asir as a result of a war between the two groups. The deities explicitly referred to as vanir are Njord, Frey, Freyja, and possibly Heimdall.

Njord is the father of Frey and Freyja, with his sister, according to Snorri in Ynglinga saga, because that was the custom among the vanir. But among the asir such incestuous liaisons were not permitted, and they therefore ended with the incorporation of the two groups of gods. Scholars generally think of the vanir as gods of fertility, perhaps especially because Frey’s major moment in the mythology involves a marriage to the giantess Gerd. But a poetic formula refers to the “wise vanir,” and Thrymskvida, stanza 15, says that Heimdall can see the future, “like other vanir.”