Jormungandr (Jórmunganðir, The Midgard Serpent):
The Midgard Serpent is one of Loki’s children along with Sleipnir and Hel as examples. He started out as nothing really but a little worm, and as he grew in size, he became too huge in a relatively short period of time. In fact, it grew to such a big size that he could bite his own tail.
There is viking myths about the waves in the sea being the result of Jormungandr twisting and turning in the oceans. Also, when the time comes for Ragnarök, he will fight Thor, the thunder god.
(Note: This is only a summary)