It is difficult to talk about a Viking symbol without mentioning Thor’s hammer. 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, it is the symbol of a pagan ideology.
The creation of Mjölnir is described in the second part of the Edda called “Skáldskaparmál”:
The story begins, when Loki, being Loki, pulled 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 favourable 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 this in mind, he approached the two brothers Brokkr and Sindri.
Using malice and treachery, playing on the pride of the two brothers, Loki told them that they too would not be able 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 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.
The first of the items to be forged, was when Sindri put a pig's skin in the forge and told Brokkr to work the bellows nonstop until his return. Loki, in disguise as a fly, 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 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.
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's iconic imagery as a one handed weapon throughout Thor's religious iconography. 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:
Thor obtained the golden hair for Sif and the Mjolnir hammer.
Odin obtained the Gungnir spear and the Draupnir ring.
Freyr obtained the ship Skidbladnir and the boar Gullinbursti.
As of Loki, the grateful as the gods all agreed that Loki still owed his head to the brothers. When the dwarves approach Loki with knives, the cunning god points out that he had promised them his head but not his neck, ultimately voiding their agreement. Brokkr and Sindri contented themselves with sewing Loki's mouth shut and returning to their forge.