Uru

"Mjølnir was forged from Uru...If such weapons into the hands of the Marauders, all the Nine Worlds could be at risk."

- Thor Uru was a god-like metal forged in the furnaces of Nidavellir.

History
The Dwarves used Uru to create several powerful weapons including Mjolnir, the Bloodaxe and the Sword of Torunn.

The Dark Elves attacked Nidavellir, stealing the Bloodaxe and the Sword of Torunn. Thor and his allies tracked them down and recovered them.