In Norse mythology, Gullinborsti (Golden Bristles) is a giant golden boar that inhabits Midgard. It was created by the dwarves Brokk & Eitri as a wager against the god Loki.
Its organization, discipline and strength were envied by all against whom it battled. Some say that Gullinborsti was Midgard's greatest nightmare.
When Loki acquired the golden hair of Sif, Freyr's ship, Skidbladnir and Odin's Gungnir spear made by the Sons of Ivaldi, he bet his own head with Brokk that his brother Eitri (Sindri) would not be able to make items to match the quality of those mentioned above.
So to give Freyr a present, Eitri threw a pigskin into the furnace, and together with Brokk, he worked on the bellows, making the Gullinborsti boar, which had bristles in its mane that glowed in the dark.
According to Húsdrápa, Freyr rode Gullinborsti at Baldr's funeral, while in Gylfaginning, Snorri states that Freyr rode in a chariot pulled by the boar.
The boar is also known as Slíðrugtanni.
The story of its creation is related in the Skáldskaparmál section of the Edda prose.