In the early 1900s a family of Norwegians, a family of Finns, and a couple Irish families hopped on some boats and decided to come here to America. For some reason they thought it was a good idea at the time. The two Nordic families and the two Irish families eventually merged together and had children. One of the Nordic sons met up with one of the Irish daughters one day, and even after being shot through the head with an arrow, the Nordic son still managed to further the Viking legacy with the (Viking) Irish daughter. In Nineteen Hundred and Eighty Two years after the Christians somehow monopolized calendars, the new Viking son was born. On that day, his awakening into life sent shockwaves back through time that rewrote history, for the Roman Emperor Caesar was killed and the phrase "Beware the ides of March!" became legend. Gleipnir, the fetters of Fenrir started to fray, and the first of the Jötnar started to open their eyes. Noting that Ragnarök was fast approaching, the Æsir saw this new great Viking presence arising. Out of Asgard, Mjölnir the hammer of Thor landed in an area of Midgard known as Maynard Massachusetts, right near the now coming of age Viking's home. Upon finding Mjölnir the hammer glowed, lightning struck as his hand grasped the handle and he was imbued with all the power of a god.
So yeah, that's pretty much it I guess.