Kraken of Myth
The legend may actually have originated from sightings of real giant squid that are variously estimated to grow to 13–15 m (40–50 ft) in length, including the tentacles. These creatures normally live at great depths, but have been sighted at the surface and have reportedly attacked ships.
The 13th century Old Icelandic saga Örvar-Odds saga tells of a massive sea-monsters called Hafgufa. The hafgufa is believed to be a reference to the kraken:
"Now I will tell you that there is a sea-monster called the hafgufa (sea-mist). Whales are the biggest of everything in the world, but the hafgufa is the greatest monster occurring in the water. It is its nature that it swallows both men and ships and whales and everything that it can reach. It is submerged both by day and night, and when it strikes up its head and nose above the surface, then it stays at least until the turn of the tide. Now, that sound we sailed through? We sailed between its jaws, and its nose and lower jaw were those rocks that appeared to you in the ocean, Ǫgmundur Floki has sent this creature to you by means of his secret arts for to cause the death of you and all your men. He thought that more men should have gone the same way as those that had already drowned, and he expected that the hafgufa would have swallowed us all. Today I sailed through its mouth because I knew that it had recently surfaced."
Old Norwegian Kraken
After returning from Greenland, the anonymous author of the Old Norwegian scientific work Konungs skuggsjá (circa 1250) described in detail the physical characteristics and feeding behavior of these beasts. The narrator proposed there must only be two in existence, stemming from the observation that the beasts have always been sighted in the same parts of the Greenland Sea, and that each seemed incapable of reproduction, as there was no increase in their numbers.
"There is a fish that is still unmentioned, which it is scarcely advisable to speak about on account of its size, because it will seem to most people incredible. There are only a very few who can speak upon it clearly, because it is seldom near land nor appears where it may be seen by fishermen, and I suppose there are not many of this sort of fish in the sea. Most often in our tongue we call it hafgufa. Nor can I conclusively speak about its length in ells, because the times he has shown before men, he has appeared more like land than like a fish. Neither have I heard that one had been caught or found dead; and it seems to me as though there must be no more than two in the oceans, and I deem that each is unable to reproduce itself, for I believe that they are always the same ones. Then too, neither would it do for other fish if the hafgufa were of such a number as other whales, on account of their vastness, and how much subsistence that they need. It is said to be the nature of these fish that when one shall desire to eat, then it stretches up its neck with a great belching, and following this belching comes forth much food, so that all kinds of fish that are near to hand will come to present location, then will gather together, both small and large, believing they shall obtain there food and good eating; but this great fish lets its mouth stand open the while, and the gap is no less wide than that of a great sound or fjord, And nor may the fish avoid running together there in their great numbers. But as soon as its stomach and mouth is full, then it locks together its jaws and has the fish all caught and enclosed, that before greedily came there looking for food."
Since the late 18th century, kraken have been depicted in a number of ways, primarily as large octopus-like creatures, and it has often been alleged that Pontoppidan's kraken might have been based on sailors' observations of the giant squid. In the earliest descriptions, however, the creatures were more crab-like than octopus-like, and generally possessed traits that are associated with large whales rather than with giant squid. Some traits of kraken resemble undersea volcanic activity occurring in the Iceland region, including bubbles of water; sudden, dangerous currents; and appearance of new islets.
Kraken Sonnet by Alfred Tennyson
In 1830 Alfred Tennyson published the irregular sonnet The Kraken, which described a massive creature that dwelled at the bottom of the sea:
Below the thunders of the upper deep; Far far beneath in the abysmal sea, His ancient, dreamless, uninvaded sleep The Kraken sleepeth: faintest sunlights flee About his shadowy sides; above him swell Huge sponges of millennial growth and height; And far away into the sickly light, From many a wondrous grot and secret cell Unnumber'd and enormous polypi Winnow with giant arms the slumbering green. There hath he lain for ages, and will lie Battening upon huge seaworms in his sleep, Until the latter fire shall heat the deep; Then once by man and angels to be seen, In roaring he shall rise and on the surface die.
Pontoppidan's description influenced Jules Verne's depiction of the famous giant squid in Twenty Thousand Leagues Under the Sea from 1870.