God Tempest
According to legend, the God Tempest, or the Mother Storm, was the first Thunderstorm, which had existed since soon after the dawn of time. It raged accross the Nine Realms, moving but never abating, and growing larger and more destructive with every year.
Though it was responsible for widespread destruction through flooding, lightning strikes and wildfires, the people struck directly by lightning were all considered to be evil-doers by their communities, leading some to believe that the storm possessed a consiousness. Since it was believed to be aware, and to be the first storm, it was worshipped as a god by the early Vanir and Light Elves.
Eventually the Storm grew so powerful and desructive that Odin was forced to hold it back from reaching Asgardia using magic. Eventually it weakened, and Odin was able to trap it within a nugget of Uru which had been given to him by the King of the Dwarves.
This nugget was later returned to the Dwarves, who used it as the heart of a new Dwarven Weapon, which Odin named Mjøllnir.
The Storm Giants consider themselves the children of the Mother Storm. Odin trapping the Storm became a major point of contention between the races. Odin eventually married the Storm Giantess Grid in an attempt to broker peace.