In Scottish folklore, the giant sea serpent defeated by Assipattle was the Stoor Worm.
The Stoor Worm appears in an Orcadian legend recorded in versions from Orkney. It was so enormous that its body could encircle the world, and its breath spread disease and destruction. The monster demanded sacrifices from the people, including young victims.
Assipattle, a seemingly ordinary farmer’s son, entered the creature by sailing into its mouth. He reached its liver and burned it, causing the Stoor Worm to die. Its body became landforms and islands, while its teeth became rocks in the sea. The story therefore explains geography as well as celebrating cleverness over brute strength.
The Stoor Worm is not the same as the Lambton Worm, a separate northern English legend, or the kraken of Scandinavian maritime lore.