Ymir

Ymir, a frost giant and the largest creature to have ever existed according to Norse mythology. The god Odin and his brothers killed Ymir and made the world from his body. His blood became the sea, his flesh the earth, his bones the mountains and rocks, and his hair the trees. Finally they placed his skull over the world as a protecting dome, and threw his brain up in the air. That's the clouds.

I've written a more detailed description on my blog here: [link]