Bölþorn (Old Norse "evil thorn") is a frost giant in Norse mythology. His parentage is unknown. He is best known as the maternal grandfather of the god Odin.
In English, his name is also written as Bolthorn or Boelthor.
Attestations
In the Poetic Edda, it is said about Bölþorn and his children:
Bestla is the mother of Odin, Vili and Vé by Borr. Bölþorn's son could be the wise being Mímir.
Gylfaginning, the first section of the Prose Edda, states that Bölþorn is a giant and the father of Bestla.
References
Bölþorn Wikipedia(Text) CC BY-SA