The weapon was forged by the Huldra Brothers Brok and Sindri, back when they were relatively unknown blacksmiths, eager to make a name for themselves. Presenting the hammer to Thor, it quickly became the deadliest and favourite weapon of the Aesir, ensuring their dominance and allowing the Thunder God to massacre scores of Jötnar with devastating ease.
After seeing the destruction wrought on giants with the very weapon they created, the two brothers suffered a profound sense of guilt. As a way to try and make up for their mistake, they then forged the Leviathan axe, a weapon capable of rivaling even Mjölnir and gave it to the last guardian of the giants left in Midgard; Laufey.
The hammer is extremely powerful, capable of killing most beings with one hit and channeling a vast amount of electricity.
- Noted as the hammer's only flaw, the handle was made too short due to a fly biting Brok on one of his eyes during the forging of the hammer.
- Despite possibly being the greatest weapon in all of the Nine Realms, only rivaled by the Leviathan and Surtr's sword, Odin is capable of making certain things indestructible even by it, as according to Mimir the tree he is imprisoned in cannot be destroyed even by Mjölnir. He also comments that the hammer can't even destroy the thick ice caused by Thamur's dying breath.
- In Norse mythology, Thor has a pair of magic gauntlets and a belt that he always wore when wielding the hammer. The belt was named Megingjörð ("power-belt") doubled Thor's already divine strength which allowed him to use Mjölnir to even greater efficiency. The gauntlets were named Járngreipr ("iron grippers") and are needed to be worn in order to wield the hammer properly, due to its short handle.
- Though Brok and Sindri express guilt for all the destruction brought about by Thor's use of their hammer, they still acknowledge it as their greatest work, albeit bitterly.
- The hammer appeared before in God of War: Ascension's Multiplayer as an add-on and possible nod to the future of the franchise. This, however, is the Canon version of the hammer.
- In Norse mythology, Magni and Modi were said to have inherited the hammer together, as it was so heavy it required both of them to wield it effectively. This does not appear to be the case in God of War, however, as they are in open competition for the hammer and both Magni and Modi were killed by Kratos and his son Atreus, leaving no inheritor for the hammer.