Kraken is a legendary sea monster of giant proportions that is said to dwell off the coasts of Norway and Greenland. The legend may have originated from sightings of giant squid that are estimated to grow to 13–15 m (40–50 ft) in length, including the tentacles. The sheer size and fearsome appearance attributed to the kraken have made it a common ocean-dwelling monster in various fictional works.
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. The Kraken is also depicted to have spikes on its suckers. 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.