Fjorgyn and Fjorgynn

In Norse mythology, the feminine Fjörgyn or Jörð (Old Norse "earth" ) is described as the mother of the thunder god Thor, son of Óðinn, and the masculine Fjörgynn is described as the father of the goddess Frigg, wife of Odin. Both names appear in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. A number of theories surround the names, and they have been the subject of scholarly discourse.

Attestations
Fjörgyn is attested in the Poetic Edda poem Hárbarðsljóð stanza 56 and Vǫluspá stanza 56. Fjörgynn is attested in the Prose Edda books Gylfaginning chapter 9, and Skáldskaparmál chapter 19, and the Poetic Edda poem Lokasenna stanza 26. The name Fjörgyn also appears in Skaldic poetry at times as a synonym for "earth" or "land."

Divine pair
Hilda Ellis Davidson theorizes that Fjörgyn and Fjörgynn may have represented a divine pair of which little information has survived, along with figures such as the theorized Ullr and Ullin, Njǫrðr and Nerthus, and the attested Freyr and Freyja.

Fjörgyn and Jörð
Rudolf Simek states that Fjörgyn may simply be another name for Jörð, whose name also means "earth," since she does not appear listed in the Prose Edda as a unique goddess, but that the fact that she does not appear elsewhere in Skaldic poetry "as would be expected of a purely literary alternative to Jörð" may be notable.

Proto-Indo-European basis
Theories have been proposed that Fjörgyn (Proto-Germanic: *Fergunaz) may represent an extension of an earlier Proto-Indo-European thunder or rain god or goddess due to Indo-European linguistic connections between Norse Fjörgyn, the Hindu rain god Parjanya, the Lithuanian god Perkūnas, and the Slavic god Perun.