The Kraken is usually referred to as a massive octopus or squid attacking ships, thought to be living off the coast of Norway. At one point, a group of fishermen caught at giant squid about 34 feet long, with eyes the size of a tractor tire. Giant squids this big are thought to be the origin of the old Norwegean legend. There have been many reported sightings of the Kraken, especially from old sailor stories. Although it seems more reasonable for the Kraken to be octopus, all research conducted and info collected leads to the conclusion that the Kraken is a massive giant squid. The size scale for the species of squid (that I know of) is:
1. Kraken
2. Colossal Squid
3. Giant Squid
4. Squid
The colossal squid is a huge squid, (once again possibly the origin of the Kraken legend.) It can also be called the Antartic or Giant Cranch Squid. The colossal squid can be referred to as an Antarctic Squid becuase it is usually found near the Antarctic waters, everywhere below the border-line of South America. The colossal squid is thought to be the largest known species of squid in terms of mass. There are many sperm whales swimming around that carry scars on their backs, and scientists think that they are the scars of colossal squid hooks from fights with squid. (The squid is the sperm whales' favorite snack.)

This is a picture of a "War Kraken" from fictional artistry.

This is a picture of the "Kraken" from the Disney Online Game: "Pirates Online."

This is a computer generated image of a theory statment displaying how the Kraken catches it's prey.