In Norse mythology, Brokkr (Old Norse "the one who works with metal fragments; blacksmith," anglicized as Brokk) is a dwarf who is the brother of Eitri (also known as Sindri).
According to the Skáldskaparmál, Loki commissioned the Sons of Ivaldi to create various items, including Sif's hair, Freyr's ship Skíðblaðnir, and Odin's spear Gungnir. Loki boasted extensively about the remarkable creations made by the Sons of Ivaldi and belittled the abilities of other dwarves, claiming that they couldn't produce anything beautiful or useful. Brokkr, who happened to be in Asgard at the time, challenged Loki's claim, asserting that his brother Eitri was capable of crafting items of superior craftsmanship to Skíðblaðnir or Gungnir. Brokkr even wagered his own head against Loki's that Eitri could create better items.
While Eitri used magic in a forge with extreme heat, Brokkr operated the bellows to maintain the perfect temperature for the enchantments. While crafting the boar Gullinbursti, a gadfly, often thought to be Loki himself, repeatedly bit Brokkr's hand. Brokkr remained undisturbed and continued to blow into the fire. During the creation of the golden arm ring Draupnir, the gadfly returned and bit Brokkr on the neck, but he persevered. Finally, when making the hammer Mjölnir, the gadfly bit Brokkr on the eye, causing him to briefly pause in his blowing. This interruption led to Mjölnir's handle being shorter than intended, which is why Thor had to wear the iron gauntlets Járngreipr to wield it safely.
Eitri succeeded in making the golden ring Draupnir, the golden-bristled boar Gullinbursti and the hammer Mjölnir. These objects were judged by the gods to be superior and Brokkr won the bet. However, Loki did not allow him to take his head as doing so would have damaged his neck which was not included in the bet. In lieu of this, Brokkr sewed Loki's lips so that Loki would not brag until the thread came out.