The giant sea monster traditionally said to attack ships is the kraken.
The kraken belongs chiefly to Scandinavian and Norwegian maritime folklore. It was said to appear in the waters off Norway, where its enormous body or tentacles could threaten vessels. The familiar image of a tentacled monster dragging ships beneath the waves developed through later travel accounts, illustrations, and popular literature.
Early written references include a 1646 Norwegian glossary, followed by descriptions from Francesco Negri in 1700 and Hans Egede in 1734. The Danish bishop Erik Pontoppidan’s 1753 account helped make the creature widely known, describing it as a gigantic animal capable of pulling ships down.
The kraken is often loosely called a creature of Norse mythology, but its best-documented history is in later Scandinavian folklore rather than the core medieval Norse myths. Modern writers commonly connect the legend with sightings of giant squid, whose verified specimens can reach roughly 10.5 metres in length.