It has been a long-term romance between Marvel and Norse mythology, one that began in 1962, with the publication of Thor.
In 1962, Journey into Mystery #83 wasn't the debut of a hero that was bombarded by cosmic rays--or even gamma rays. This new hero wasn't bitten by some radioactive spider or simply born with powers that implicate an evolution of the human species.
This hero was a god. Specifically, he was a Norse god.
The debut of Thor, God of Thunder, marked the beginning of the Norse mythology's reign of influence in Marvel Comics. That influence continues today, whether in the pages of the character's popular main title or next summer's much-anticipated film adaptation.
Marvel Comics isn't the only venue to recognize and incredibly alter the Norse mythos. Works with nods to the Norse include the fiction of J.R.R. Tolkien, several video games referencing the universe-ending Ragnarok and black metal bands who have somehow found a connection between pinched harmonics and viking war song.
The Marvel incarnation of Thor would pull in several aspects of the character's Norse roots, including the mighty hammer Mjollnir, all-powerful father Odin and mischievous step-brother Loki and several others as the character's narrative progressed and changed through the years.
Of course, Thor isn't the only character that has been plucked from various mythologies either in a stroke of brilliance or utter laziness by creators.
A quick glance at Marvel's hero roster would bring the likes of famed Olympian Hercules, introduced as a rival to the God of Thunder and Ares, God of War and Awkward Thought-Bubbles in the pages of The Mighty Avengers . The roster of villains in the Marvel Universe is just as infested with mythological likenesses.
To this day, creators attempt to marry Thor's historical roots with the shape his story has taken from the House of Ideas. The wiggle room a writer gets with a religion few subscribe to is something that has been discussed in this blog several times.