There are few Viking symbols so emblematic as the Thor's Hammer, the Mighty Mjölnir.
The hammer’s name, Mjölnir, comes from the proto-Germanic form meldunjaz, from the Germanic root of malanan "to grind" (melwan, Old Icelandic meldr, mjǫll, mjǫl "meal, flour"), yielding an interpretation of "the grinder; crusher”, an apt name for the mightiest hammer of all.
Thor’s hammer also symbolizes power, strength and bravery, being an amulet of protection and luck. Today it also symbolizes belonging to a community, being one of the most iconic the symbols of worshiping the Old Gods.
The creation of Mjölnir is described in the second part of the Edda called “Skáldskaparmál”:
The story begins, when Loki, being Loki, shows little common sense and decides to pull a prank on the Goddess Sif, Thor’s wife, by cutting off her beautiful golden hair while she slept.
As expected, Thor entered into an unparalleled anger and, not for the last time, threatened to end Loki’s life.
Loki was many things - including for a brief time the mare that gave birth to Odin’s steed, Sleipnir - but the God of mischief was not crazy nor stupid and, fearing for his life, quickly sought to apologize for his prank.
To make amends, Loki asked Thor for permission to go see the dwarves, being the best blacksmiths in the cosmos, and promised to bring back to Sif a hair even more beautiful than the original one, as well as other treasures for the Gods.
In the realm of the Dwarves, Svartalfheim, Loki met the sons of the dwarf Ivaldi. They not only forged her golden hair for Sif, but also two other treasures:
A magical boat, the best of all, able to bend in a pocket and always offering a favorable wind for sailing named Skidbladnir, which means “Assembled from Thin Pieces of Wood”, and a powerful magical spear, with runes engraved on the tip, the deadliest spear in the universe. Its name is Gungnir meaning “Swaying”.
Loki’s mission was a success and he could have returned directly and offered Thor the means to redeem himself.
Loki, however, could not resist the urge to stay longer and try to get more treasures forged by these talented dwarves.
With trickery in mind, he approached the two dwarven brothers Brokkr and Sindri and taunted them, claiming that they lacked the skills to create three objects as wonderful as those of Ilvaldi’s sons.
Loki even went so far as to bet his own head on it, a prize that the dwarves could not resist - for Loki's annoyance was well known through all the Nine Realms.
The dwarves began to work immediately, and with such craftsmanship that made the God of mischief rethink his hasty bet. As Loki was very attached to his head, he decided to sabotage the dwarves efforts, by turning into a fly in order to distract the dwarves.
For the first of the items to be forged, Sindri put a pig's skin in the forge and told Brokkr to work the bellows nonstop until his return. Disguised as a fly, Loki comes and bites Brokkr on the arm to ensure the brothers lose their bet. Nevertheless, Brokkr continues to pump the bellows as ordered. When Sindri returns and pulls their creation from the fire, it is revealed to be a living boar with golden hair which they name Gullinbursti. This legendary creature gives off light in the dark and runs better than any horse, even through water or air.
Next, Sindri puts gold in the forge and gives Brokkr the same order. Loki comes again, still in the guise of a fly, and bites Brokkr's neck, this time twice as hard to ensure the brothers lose the bet. Brokkr, however, continues to work the bellows despite the annoyance and pain. When Sindri returns, they draw out a magnificent ring which they name Draupnir. From this ring, every ninth night, eight new golden rings of equal weight emerge, ensuring abundance for its owner.
Finally, Sindri puts iron in the forge and repeats his previous order once more. Loki comes a third time and bites Brokkr on the eyelid even harder, the bite being so deep that it draws blood. The blood runs into Brokkr's eyes and forces him to stop working the bellows just long enough to wipe his eyes. This time, when Sindri returns, he takes Mjölnir out of the forge.
The handle is shorter than Sindri had originally planned, which is the reason for the hammer to be a seemingly unbalanced weapon. Nevertheless, the pair are sure of the great worth of their three treasures and they make their way to Asgard to claim the wages due to them.
Loki preceded them and presented to the Gods the wonders acquired during his journey. The Gods agreed unanimously (with the exception of Loki) that the hammer, Mjolnir, despite its short handle, was the finest object ever made, much to Loki's despair, who realized he was about to lose his head over his bet with the dwarves. While Loki formulated a new plan to escape his demise, the Gods divided the treasures amongst themselves:
Lady Sif obtained the golden hair.
Thor, his Mjolnir hammer.
Odin obtained the Gungnir spear and the Draupnir ring.
Freyr obtained the ship Skidbladnir and the boar Gullinbursti.
When the Gods finished claiming the treasures, The dwarven brothers claimed the price Loki himself had agreed for them: his head.
When the dwarves approach Loki with knives, the cunning God puts his plan in motion and points out that he had promised them his head, but not his neck. The dwarves could not claim the former without damaging the latter, ultimately voiding their agreement.
The dwarven brothers were denied Loki's head, but would claim compensation from their deeds. With the consent of the Gods, the brothers sewed Loki's mouth shut, so it could not spew schemes and lies - at least for a time - and decided to return to their forge.
Simek, Rudolf. 2007 (1993). Translated by Angela Hall. Dictionary of Northern Mythology. D.S. Brewer. ISBN 0-85991-513-1
Orchard, Andy. 1997. Dictionary of Norse Myth and Legend. Cassell. ISBN 0-304-34520-2
Jesse Byock (2005) Snorri Sturluson, The Prose Edda. 1st. edition. London, England: Penguin Books Ltd. ISBN-13 978-0-140-44755-2