In Norse mythology, the feminine Fjörgyn (Old Norse "earth") is described as the mother of the thunder-god Thor, son of Odin, 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.