Norse mythology is the body of pre-Christian myths and religious beliefs of the Norse-speaking peoples of Scandinavia and Iceland: the stories of gods like Odin, Thor, and Loki, of the world-tree Yggdrasil, and of Ragnarök, the foretold end of the world. Most of what survives was written down by Christian Icelanders two centuries after the North converted, above all in the two works known as the Eddas.
Most mythologies let their gods win in the end. Norse mythology tells its gods, plainly, that they are going to lose. A day is coming when the monsters break loose, the gods fall one by one, and the world burns and sinks into the sea. The gods know all of this is their fate. They forge their weapons and train their heroes for a last battle they have already been told they cannot win. That defiance, in the teeth of a doom no one can stop, is the strange heart of these stories.