The Old Mother

The Old Mother was an ancient Kraken who inhabited the Sea of Thieves centuries before the first pirates arrived to sail the seas. Colossal in size and more akin to a cosmic horror than a leviathan, the Old Mother was said to have been bigger than any outpost and had the ferocity to match. Upon her death, her children scattered and went into hiding. Now only one is known to be active. However, due to their time spent immobile, the Krakens of old are encrusted into the reefs they rest in and are almost impossible to find unless stirred from their deep slumber by an outside force.

Backstory
Not much is known about the Old Mother's history, but myths and legends provided by Sudds in the Stars of a Thief Tall Tale as well as the Athena's Fortune novel suggest that she ruled the waves well before the arrival of the Ancients. She is the mother of all Krakens, living and dead, and once terrorized the Merfolk. As the hands of time marched on, she even began to threaten the Ancients. So great was the threat she posed that the Ancients and the Merfolk found common ground to actively collaborate with one another in hopes of combatting her. It seems that multiple approaches were attempted. From Ancient cave paintings seen on Devil's Ridge and Cannon Cove, the Ancients seem to have been attempting to make offerings to her, as they believed her a living god that could be appeased. This was unsuccessful, and the Ancients who attempted this were slaughtered. The Old Mother proved far too large and far too powerful to be slain properly, so the Ancients and Merfolk worked together to come to a new solution. Using the Ancients' knowledge of advanced magic and the Merfolk's mastery over the waves, magical chains were constructed which would not rust and could not be broken by any force, no matter how powerful, and used to chain the Old Mother as she entered her rest. These chains proved highly effective, though the Old Mother would not relent so easily. The Old Mother awoke, and was said to have thrashed for a century before eventually starving to death. From here, her children scattered across the sea and presumably died out. An untold amount of years later, Ramsey Singh along with the crew of the Magpie's Wing found her skeleton laying in the northern Wilds and took the chains wrapped around her ancient bones to construct the chests pirates can loot in the present day.

Trivia

 * According to the legends Sudds has documented in Stars of a Thief, the Old Mother's name is literal. Krakens are referred to as 'siblings' in a poem.
 * The Shroudbreaker is fashioned in the shape of a Kraken, and the logo for the Ancient Isles has the Old Mother's celestial symbol on it.
 * Much of the Ancients' architecture, mainly arches and beams, implement Kraken tentacles in their design.
 * Kraken's Fall, when viewed at from a map, strongly resembles a behemoth Kraken skull laid upside down.
 * The model of the Captain's Chest has motifs that strongly resemble the Ancient design for Kraken tentacles. This may harken back to the origins of the metal used to create them.