Gullinbursti (meaning "Gold Mane" or "Golden Bristles") is a boar in Norse mythology.
When Loki had Sif's hair, Freyr's ship Skíðblaðnir, and Odin's spear Gungnir fashioned by the Sons of Ivaldi, he bet his own head with Brokkr that his brother Eitri (Sindri) would not have been able to make items to match the quality of those mentioned above.
So to make gifts to Freyr, Eitri threw a pig's skin into a furnace as Brokkr worked on the bellows, and together they manufactured the boar Gullinbursti which had bristles in its mane that glowed in the dark.
The story of Gullinbursti's creation is related in the Skáldskaparmál section of Snorri Sturluson's Prose Edda.
Sindri laid a pigskin in the hearth and bade Brokkr blow, and did not cease work until he took out of the hearth that which he had laid therein. But when he went out of the smithy, while the other dwarf was blowing, straightway a fly settled upon his hand and stung: yet he blew on as before, until the smith took the work out of the hearth; and it was a boar, with mane and bristles of gold. ... Then Brokkr brought forward his gifts: ... to Freyr he gave the boar, saying that it could run through air and water better than any horse, and it could never become so dark with night or gloom of the Murky Regions that there should not be sufficient light where he went, such was the glow from its mane and bristles.