Thor was a young Norwegian from centuries past. He lived in the wilderness with his mother and father -- though not Odin or Friga as commonly believed. This Thor was scrawny and sickly and often teased by his peers. His father tried to toughen him up, but Thor preferred to hide away in the wilderness and living the life of a hermit.
Thor discovered a secret cave. There was an eerie light within that cave, which Thor liked to basked under during his daily meditations. Strangely, this energy caused Thor to slowly transform into a muscle-bound hunk! Not only that, but Thor discovered a hammer-shaped chunk of metal within the cave that literally hummed with energy! Not only that, but it created a huge mess when thrown at other objects!
Soon enough, the Huns invaded Norway. I don't remember that battle too much from my history books, but this is the reason for that. The Huns discovered Thor communing with nature and decided to attack the young Norwegian. That didn't go over very well.
The surviving Huns were quickly chased away and Norway was saved! Thor was free to commune with nature again. And the mysterious cave has remained a secret ever since!
I keep thinking that it would be great to read more stories about the Hammer of Thor. He has the potential to be something big. We have a template here, but not much else. Somebody could do something really great with Thor and his crazy hammer.
Maybe that somebody could be me...