Miðgarðsormr

Miðgarðsormr, also known as Jǫrmungand, gigantic serpent from Norse mythology.

Quotes about Miðgarðsormr:

 * The great sea is held together by Jörmungand, the serpent who surrounds it with his gigantic body and who holds his tail in his mouth to complete the circle, and thus stops the waves from forming. One day, the god Thor, son of the earth, was fishing in the serpent sea, using an ox's head as bait. Jörmungand reared up, and the waves hit the shores as he twisted and writhed like a fury. They were equally strong, the serpent and the god in that furious struggle. The sea boiled around them, but then the hook was removed and the snake slithered free and quickly sank beneath the waves again. And soon the sea was calm again as if nothing had disturbed it. (Vikings)
 * Midgardsormen, the world serpent, will leap out of the ocean, raising the tides and submerging the land. The wolf, giant Fenrir, will break his invisible chains. [...] Thor will kill the serpent, but will die from its poison. (Vikings)

Snorri Sturluson:

 * And the serpent sank into the sea. Thor threw the hammer after him, and some say he cut off his head at the bottom, but I think I must tell you truly that the serpent of Miðgarðr still lives and lies in the ocean.
 * Then the ocean will roll over the lands, because the serpent Miðgarðr will be seized by the fury of the giants and will reach the land. [...] Miðgarðr's serpent will breathe so much poison that it will splash all the air and water, and it will be really scary, and it will stand by the wolf's side.
 * One can say that one has not seen a frightening sight if one has not been able to see how Thor pierced the serpent with his eyes and how the serpent stared back at him from below and spat venom.