The other day I asked a question on Google+ if anyone had used the Tarrasque in their game. Most had, one even said it was a playable class which boggles the mind and sounds fun as hell. Recently in my campaign the players were exploring one thing and ended up seeing the Tarrasque free itself from hibernation. They're not sure what to think of it other than not to get in its way at this point. I know what I am doing with it and how to use it, but I was thinking of different ways such a creature could be used in a campaign.
First, it is a force of nature, destroying everything in its path. It eats and sleeps. It's only purpose is to eat and sleep. There is no grand scheme to its actions other than that.
Second, it is a force of nature that does have a purpose. When things get unbalanced, because we all know nature is neutral and loves balance, this big boy comes out to play to set the scales equal.
Third, a god pet. Release the Kracken kind of thing.
Fourth, a prehistoric god itself who has outlived all its followers and now seen only as a abomination.
And I am sure there are a billion other back stories you could give this big boy. I'm still working on the mythology for mine. I've got most of it figured out, but still looking for some tasty bits. So if you have any Tarasque stores and feel like sharing please do. I want to peek at your ideas and maybe steal some ideas.
At least I am an honest thief.