Surume

The kraken is a sea monster which dwells in the deepest parts of the ocean.

Appearance
The kraken is a massive, boneless, octopus-like creature several hundred times larger than the Thousand Sunny. Unlike a regular octopus, it has a turtle-like head without a beak between the arms.

Strength
Possibly due to his size, he is demonstrated to be very powerful, with its tenticles long enough to crush several ships in one swipe. It was also shown to destroy a ship bigger than the Thousand Sunny without any effort and knock out a giant with a single punch. He was also able to knock out Wadatsumi with just one punch.

Personality
In Norse mythology, the kraken is said to have dragged dozens of sailing vessels down into the ocean to devour its crew. Indeed, when the Straw Hats first encounter one on their way to Fishman Island, several crushed pirate ships can be seen between its massive tentacles, indicating that it feeds on the ships and crew it pulls down into the ocean. Caribou recites a story about it, calling it "the enemy of the human race" and that it "never knows satisfaction where killing is concerned." He found it odd that one would be living near the Red Line. His personality appears to become more playful after Luffy taming it, such as placing the Thousand Sunny on top of his head.

History
The Straw Hat Pirates first encountered a Kraken on their way to Fishman Island. The massive creature apparently had taken shelter beneath the Downward Plume while feeding off of the passing pirate ships attempting to make their way through the Red Line for the past few days. Several crushed ships can been seen clutched between its tentacles. While the rest of the crew comments on the creature's sheer gargantuan size, Luffy, undeterred, expresses his wish to "tame the little guy" with excitement, much to Caribou's shock. Soon Coribou and the other Caribou pirates arrive and the Kraken destroys their ship.

Luffy, Sanji, and Zoro left the Sunny in Barefoot Coating bubbles introduced by Caribou in order to fight the Kraken without bursting the protective bubble around the Sunny. Before they begin their assault the Kraken attempts twice to crush the Thousand Sunny with it's tentacles but is thwarted once by "Franky Rocket Launcher" and a second time by Chopper's new and improved "Guard Point". Sanji burned one of the Kraken's arms off with Diable Jambe, followed with Zoro severing one more with a new Santōryū technique. This infuriated Luffy due to his desire tame the Kraken as a pet. Luffy then used Gear Third and imbued the attack with Busoshoku Haki. The attack knocked out the Kraken even while Luffy was being severely weakened by the seawater. The Kraken is then carried by the Downward Plunge into the blackest depths of the sea along with the trio.

Later however, when the remaining Straw Hats are under attack by Van Der Decken and the Flying Dutchman, the Kraken appears and takes out the Umibozu Wadatsumi saving Thousand Sunny's bubble from bursting. It is then revealed that the Monster Trio had tamed the Kraken and that Luffy had named it Surume.