Gullinborsti means golden bristles in Old Norse and is the boar of the god Freyr. Another name is Slíðrugtanni (dangerous tusks). The boar pulls Freyr's chariot through water and through air and often illuminates the night with its golden bristles. One then sees for a long time only the lower rows of spines, signaling that the giant boar is passing through the dark skies.
The myth of Gullinborsti is recounted in the Skáldskaparmál, part of the prose Edda.
When Loki had the four sons of Ivaldi make Sif's golden hair, Freyr's ship Skíðblaðnir and Odin's spear Gungnir, he wagered his head on Brokkr that his brother Eitri would not be able to make something so valuable.
To accomplish gifts for Freyr, Eitri then threw a pigskin into the stove while Brokkr operated the bellows, and together they made the magnificent Gullinborsti with its golden mane and bristles that glowed in the darkness and shed off golden sparkles.
Incidentally, Loki kept his head, because as he pretended, otherwise his neck would be damaged, and it was not included in the wager.
The first Swedish kings, the (Ynglinge), wore helmets with the image of a boar. One of them was called Hidisvin, which was Freya's boar. The boar helmet is also mentioned in the Anglo-Saxon poem Beowulf. Another royal heirloom was the Sviagriss, a ring with the image of a piglet.
The boar is also a common theme with its own meaning (general fertility and strength) in other mythologies.
Some mention the affinity of the English boar and bear or the Dutch bear as a sign of natural power. Names with "Bir" and "Ber" would also refer to it (as in Brigit who had a cult of her own). The Celtic Cailleach was also called Bheur.