If you thought the petrifying basilisk of Harry Potter and the Chamber of Secrets was the first slithering serpent to terrorize readers everywhere, think again. Jormungand, the gigantic sea-snake of Middle Earth, has been giving Vikings nightmares for centuries. Jormungand is the spawn of resident Asgard trouble-maker Loki and his giantess mistress, Angrboda. Not a good combo, since he inherits daddy's troublemaking nature and mommy's monstrous size.

The Asgard gods realize immediately that Jormungand's a problem child. They try to get rid of him by throwing him in the ocean surrounding Middle-Earth. Big mistake. He quickly grows so big on a daily diet of whales that he's able to encircle the whole world and bite his own tail. Yowza.

Jormungand is Thor's nemesis; the big one that the hero just can't catch. When the waters begin to ripple, watch out: it means that Jormungand has awakened, let go of his tail, and Valhalla—the end of the world—is near. Gulp.