Mjölnir

In Norse mythology, Mjölnir ( /ˈmjɒlnɪər/ or /ˈmjɒlnər/ MYOL-n(ee)r; also Mjǫlnir, Mjollnir, Mjölner or Mjølner) is the hammer of Thor, a major god associated with thunder. Distinctively shaped, Mjölnir is depicted in Norse mythology as one of the most fearsome weapons, capable of leveling mountains. Though generally recognized and depicted as a hammer, Mjölnir is sometimes referred to as an axe or club. In the 13th century Prose Edda, Snorri Sturluson relates that the Svartálfar Sindri, the brother of Brokkr, made Mjölnir while in a contest with Loki to see who could make the most wonderful and useful items for the Gods and Goddesses in Asgard.

The Prose Edda gives a summary of Mjölnir's special qualities in that, with Mjölnir, Thor:

... would be able to strike as firmly as he wanted, whatever his aim, and the hammer would never fail, and if he threw it at something, it would never miss and never fly so far from his hand that it would not find its way back, and when he wanted, it would be so small that it could be carried inside his tunic.