It was worshiped as a god in times past, then as the main servant of the sea god. Sacrifices were driven to the shores in the long ago past, then put on boats to be devoured in a great display of the raw, destructive power of nature. There were wars on land and the tribute stopped. Ships became bigger and started fighting back when it tried to take them. It started taking them just to take them, to remind the people that it was what ruled the seas. It moved to deeper waters and found larger prey. While it had always preyed on the creatures of the seas, as it grew, it’s prey grew, too. Whales changed their migration patterns to avoid it as it grew larger and larger.
It stayed deep in the ocean, feeding on the wildlife and remembering when the humans had worshiped it. After a while, it became nothing more than a legend to the people on the land. The sea was something to be tamed, the creatures of the sea to be hunted, and the humans would sail all over the world. In the deep of the ocean, it slept, dreaming wild dreams of the long-forgotten past.
The humans explored and found other lands. In their greed, they brought war to the ocean. Great battles were pitched along the shores for the treasure that was found across the sea. When they met out over the deep ocean, the rumble of cannon and the occasionally sinking ship woke the great beast of the deep. It began to crush the ships as they sank near its resting place and devour the humans it found inside. As the battles became larger and more frequent it swam higher and higher until, in the midst of the largest battle of the age of exploration, it used its great tentacles to grab one of the ships and pull it down to the depths.
It was able to grab three more ships before the humans turned their cannon on it, their war with each other forgotten. The ammunition bounced harmlessly off or fell ineffectually into the sea. It descended deep into the sea to enjoy the bounty it had claimed and became the god it had once been. There were other ships, convinced that there was no real danger in the middle of the ocean. Some made it past without incident, others were not so lucky. It took its tribute when it wanted it and allowed the humans to worship it in fear.
However, it had been too long for the humans to remember worshiping the sea. They were determined to have their way in the world and soon, the ships no longer rode the waves as they crossed to the new world. The great god of the deep sea had to come to the surface to take the floating tribute and it didn’t like it. Exposing itself to the air made it vulnerable but it had come to remember its past and wanted more. It hunted more, and farther, than it ever had and the ocean was occasionally red with the blood of its prey. Those ships that braved the waves were subject to brutal attacks, but it was less certain when they would occur. If they were very lucky, they could get across with almost no incident.
Then, when it went to attack another ship, the humans fought back. While the cannon had been largely ineffectual, the new weapons bit sharply and it was forced to retreat. Many of the ships that crossed were armed with such weapons and it was never sure when they were going to be used. It stayed out of certain areas of the ocean and continued trying to attack the ships in the air, that seemed to be going higher and higher away from the ocean.
It hungered for tribute and could no longer stand the ocean depths that had hid it for so long. Its limbs became weak and did not obey they way they used to. It couldn’t hunt the prey it needed to stay strong and it couldn’t go back to sleep. Then, the ships with the weapons came looking for it.