Introduction
Njord is a god of the sea, seafaring, fishing, wealth and prosperous winds, a member of the Vanir, the second family of Norse gods, associated more with fertility and prosperity than the more warlike Aesir. He was sent to live among the Aesir as a hostage to seal the peace after the Aesir-Vanir War, along with his children Freyr and Freyja.
This article follows Old Norse mythological tradition, chiefly the Poetic Edda and Snorri Sturluson's Prose Edda, noting where the two sources differ.
Family
The Aesir-Vanir War
The two families of gods, Aesir and Vanir, fought a long, inconclusive war, eventually ending in a truce sealed by an exchange of hostages: the Vanir sent Njord, along with his children Freyr and Freyja, to live among the Aesir, while the Aesir sent Hoenir and Mimir to the Vanir.
Marriage to Skadi
After the giant Thjazi's death (killed by the gods for kidnapping Idunn), his daughter Skadi came to Asgard seeking compensation. As part of the settlement, she was allowed to choose a husband among the gods, but only by looking at their feet; she chose the feet she judged most beautiful, believing them to belong to Baldr, but they turned out to be Njord's. The marriage did not last: Njord, accustomed to his home by the sea, Noatun, could not bear the mountain howling of wolves at Skadi's home, Thrymheim, and she in turn could not bear the crying of seabirds at his, and the two eventually parted, living apart.
Family
According to Snorri, among the Vanir it was customary for siblings to marry, and Njord's own sister, unnamed in the sources, was traditionally both his wife and the mother of Freyr and Freyja, before he went to live among the Aesir.