Sister-wife of Njörðr

In Norse mythology, the sister-wife of Njörðr is the unnamed wife and sister of the god Njörðr, with whom he is described as having had the (likewise incestuous) twin children Freyr and Freyja. This shadowy goddess is attested in the Poetic Edda poem Lokasenna, recorded in the 13th century by an unknown source, and the Heimskringla book Ynglinga saga, a euhemerized account of the Norse gods composed by Snorri Sturluson also in the 13th century but based on earlier traditional material. The figure receives no further mention in Old Norse texts.

The situation is further complicated in that narratives describing the birth of Freyr and Freyja contradictorily cite the birth of the siblings occurring either after or before Njörðr left Vanaheimr to live among the Æsir. In addition, Freyr is referred to as the "son" of Njörðr and the goddess Skaði in the Poetic Edda poem Skírnismál.

In his 1 CE work Germania, Tacitus describes rituals surrounding a deity by the name of Nerthus, a theonym that is etymologically ancestral to Old Norse Njörðr. However, the figure described by Tacitus is female. Based on this scholars have suggested a Proto-Germanic hermaphroditic deity or a gender aspectual pair (similar to Freyja and Freyr), identified the obscure Old Norse goddess name Njörun as a potential name for the otherwise unnamed goddess, and in some cases identified a potential reflex of a narrative about Njörðr and his sister-wife in Saxo Grammaticus's 12th-century work Gesta Danorum.

...
Wikipedia