The Kraken's Appearance: Similar to a giant octopus or squid, though earliest stories describe it as more of a giant crab.
Symbol or Attribute: Tentacles. Fearsome determination to bring down ships and to never let go.
Strengths: Physically strong and agile. Secretive and capable of sudden attack.
Weaknesses: The Kraken is not immortal and can be killed.
Associated Sites: The Kraken originated in Scandinavian folklore, though it is not usually called by that name. While a giant octopus-type creature could certainly be part of Greek myths in the octopus-rich waters, this doesn't seem to have occurred to the Greeks. It is somewhat similar to Scylla, a genuinely Greek sea monster.
Basic Story: In the modern "Clash of the Titans" movie, the Kraken is a Titanic-era monster which is under the control of the great god Zeus, who can summon the Kraken or order the release of the Kraken; this scene from the movie was used in the promotional trailers and ads and "Release the Kraken!" briefly became a catchphrase. Normally, the Greek god Poseidon had dominion over the oceans and would be a more likely choice to summon the Kraken. But the actual Kraken is not part of any traditional Greek myth.
Interesting Fact: Some writers suggest that the legends of the Kraken may have been related to the mysterious happenings around the highly volcanic island of Iceland, where gas bubbles could roil the sea and poisonous vapors rise up unexpectedly. Greece also has its share of volcanic islands, including Santorini, Milos, and Nyssiros.