In Norse mythology, Sif is a golden-haired goddess associated with the earth. She is attested in the Poetic Edda, compiled in the 13th century from older traditional sources, the Edda of Snorri and Scalde's poetry. In both Eddas she is known for her golden hair and is married to Thor.
Snorri's Edda tells of Sif once having her hair cut off by Loki and Thor forcing Loki to have a golden wig made for Sif, which not only gave Sif's golden hair but also five other magical and powerful items for the gods.
She is related to the prophetess Sibyl and could transform herself into a swan. Sif is one of the Aesir, and the wife of Thor. With him, she had Thrud. She is also the mother of Ullr, by an unspecified father.
In the story of Aegir's feast, where Loki curses all the gods, Loki reveals that Sif once cheated on Thor. But otherwise she is considered a chaste and faithful wife.
Some sources report that Sif can see into the future, but this is not mentioned in the Edda poems. In some of the older Germanic sources it is mentioned that Sif is a swan goddess, and that she can therefore take this form.
Sif is also one of the heroines in the Marvel Comics comic "Thor". In the 2011 film adaptation of the comic, Sif is played by actress Jaimie Alexander.