Thor's mighty hammer, granting him many superpowers such as weather manipulation (especially casting thunderbolts), flight, energy manipulation, teleportation, etc. It was enchanted so that only the righteous and worthy may wield it and possess the power of Thor (not even Thor himself is exempt from this requirement, and there have been several instances in the comics and related media where he was deemed (temporarily) unworthy).
Unlike most war hammers in fiction and real life, this version of Mjölnir more resembles an oversized mallet with a relatively short handle.
