Norse mythology has exactly one divorce, and it is about the commute.
Skaði has been given a husband as legal compensation for her father's death, and the marriage begins with a bargain about where to live. They agree to split it: nine nights in her home Þrymheimr, in the mountains, then three — or in some readings nine — in his, Nóatún, on the shore. Neither can stand the other's country. Njörðr comes back from the fells complaining that the howling of wolves was hideous compared to the song of swans, and that he could not sleep for it. Skaði says she could not sleep on the sea-bed for the screaming of the gulls waking her every morning. So she goes back to the mountains and he stays by the water, and the sources simply leave it there, with no blame assigned to either party and no reconciliation attempted.
It is the least mythological quarrel in the corpus and by some distance the most recognisable.
Nóatún, and what a sea-god was for
His hall is Nóatún — "ship-enclosure," the place where boats are drawn up. Snorri's summary of him is not about storms or drowning but about control: he governs the course of the wind, stills sea and fire, and is invoked for voyages and for hunting at sea. And then the sentence that matters: he is so wealthy that he can grant land and moveable goods to whoever asks, and men should pray to him for these.
That is not a nature deity. That is a god of maritime prosperity, of the ship that comes back loaded, in a society where seaborne trade and raiding were the mechanism by which a family became rich. Drowning belongs to Ægir and Rán; the sea as an economy belongs to Njörðr.
He is invoked with his son in the standard Icelandic legal oath — by Freyr and Njörðr and the almighty áss — which puts him in the operative language of the courts rather than only in poetry. Place-names support a genuine cult: Njarðvík in Iceland and Norway, Nærøy, Njardarlög, Nærdhæwi and a scatter of Swedish forms, concentrated on coasts and fjords.
Nerthus, and a problem across a thousand years
Tacitus, writing Germania around 98 CE, describes seven tribes on the Baltic coast who jointly worship Nerthus, whom he glosses as Terra Mater, Mother Earth. She has a grove on an island; a covered wagon holds her; a priest detects when she is present and accompanies the cart through the settlements; while she travels no one goes armed and there is peace and rejoicing; afterwards the wagon, the cloth and the goddess herself are washed in a secluded lake by slaves who are then drowned in it.
Nerthus is the exact linguistic ancestor of Njörðr. The correspondence is regular and undisputed — Proto-Germanic *Nerþuz gives Old Norse Njörðr by ordinary sound change.
What cannot be explained is the sex change. A goddess of the earth in first-century Denmark becomes a god of the sea in thirteenth-century Iceland. The proposals are: a divine brother-sister pair of whom only the male survived in the north, which would fit Snorri's note that Njörðr fathered Freyr and Freyja on his own sister under Vanir custom; or a single deity whose gender was not fixed; or two separately-developed figures inheriting one name. None is provable. The Nerthus passage is the oldest detailed description of a Germanic cult anywhere, and its relationship to the Norse material is real, certain in its linguistics and completely obscure in everything else.
Hostage
Njörðr crosses to the Æsir at the end of their war with the Vanir, as a hostage — sent with his son and, in the arrangement's mirror image, exchanged for Hœnir and Mímir, which goes disastrously for the Vanir. Vafþrúðnismál adds a detail Snorri does not dwell on: Njörðr was raised among the Vanir, and at the doom of the gods he will return home to the wise Vanir.
He is therefore the only figure in Norse mythology explicitly said to survive Ragnarök by going back where he came from. Not resurrection, not inheritance — repatriation at the end of the treaty. It is a strikingly legalistic way to escape the end of the world, and it fits a god whose other appearances are all about property, oaths and settlements.
The euhemerised king
Ynglinga saga turns him into a Swedish ruler succeeding Odin, under whom the harvests were so good and the peace so complete that the Swedes credited him with both, and who was marked with the spear and burned at his death. The Ynglingar dynasty's claimed line runs through him to Freyr. This is Snorri doing history: making the old gods into early kings so they can be ancestors rather than rivals. It should not be read as mythology, but it does show which gods a thirteenth-century Icelander thought a Swedish royal house would want to claim.
What almost nothing modern does with him
He is essentially absent from film and television Norse mythology, appearing in games mostly as a name. That absence is unremarkable given that his surviving myth consists of a failed marriage and a shipyard, but it means the modern picture of the pantheon leaves out the god that a coastal trading society had the most practical daily reason to think about. For where the Vanir stand in relation to everyone else, see the Norse tradition overview and the family tree.
Did Njörðr and Skaði have any children together?
Not according to Snorri, who is clear that Freyr and Freyja were born before the marriage, to Njörðr's unnamed sister among the Vanir. Ynglinga saga, however, says Skaði afterwards married Odin and had many sons by him, one of whom, Sæmingr, became the ancestor of the earls of Hlaðir. Some later Norwegian genealogies attach Sæmingr to Njörðr instead. The disagreement is genealogical politics — competing dynasties claiming different divine fathers — rather than a mythological variant.
Why is a sea-god counted among fertility deities at all?
The category is imported. What Njörðr, Freyr and Freyja share in the sources is not "fertility" but ár ok friðr — good season and peace — a fixed formula covering harvest, calm weather, safe travel and the absence of feud, which is what a farming and trading population actually asked its gods for. Wealth from land and wealth from the sea are the same request in that framework, which is why the god of the shore and the god of the field are father and son.