When the universe was still in its infancy, the immortal creatures known as the Celestials became aware of the existence of other universes and were curious to visit them; consequently, the Celestials created a series of gems to enable themselves to traverse the dimensions, among other things. An additional stone, called the Matrix Stone, was subsequently created to control the power of the others.
Under unknown circumstances, all of these gems, with the exception of the Matrix Stone, ended up in the possession of Karnilla, the Norn Queen. Eventually becoming known in all of the Nine Realms as the Norn Stones, they were believed to have been created in Nornheim through Asgardian magic.
With Asgard vacant after the Dark Gods of Narcisson's capture of the Asgardian gods, Morgan Le Fay took the opportunity to claim several objects of power from there, including the Norn Stones and the Twilight Sword. She used the stones and the sword in conjuction with the captured Scarlet Witch's powers to rewrite reality, thus creating an alternate universe in her own image. Le Fay was ultimately defeated by the Avengers and reality was brought back to normal. Thor later retrieved the Norn Stones.
Following the Hood's depowerment, Loki presented him with the Norn Stones in order to grant him back the use of his powers. Loki later reclaimed the stones during the Siege of Asgard to give the Avengers a fighting chance against the Void, using the stones to temporarily boost their powers. Unfortunately, the Void realized his enemies' source of power and killed Loki.
Having somehow claimed one of the Norn Stones again, the Hood briefly used it in his bid to become the new Kingpin of New York. It was later stolen by Mike Murdock, a human fragment brought into existence on accident through the power of Reader. Using a book of Asgardian spells he had hired Black Cat to steal, he used the stone to rewrite history and make himself a real person.
According to Loki, the effects of the Norn Stones vary from person to person, depending on whether the stones accept the user, and what they desire.
Alternate Reality Versions
Ultimate Universe (Earth-1610)
In this reality, the Norn Stones were made of the same substance as Mjolnir, and were the "avatars of power" for Asgard. There were 24 sacred runes that, when placed in proper sequence in an access portal in northern Germany, allowed gates to open to seven accessible realms, as well as a "room with no walls". Loki used the stones to launch a massive invasion of Earth through Central Park.
Avengers: Earth's Mightiest Heroes (Earth-8096)
In this reality, the Norn Stones were a set of nine powerful magical artifacts created by Karnilla, the Norn Queen. Amora the Enchantress and Baron Zemo planned to use the Norn Stones to concur Earth. Zemo sent his Masters of Evil to specific locations across the globe to open portals to the Nine Realms. With the Norn Stones, Zemo was able to scatter the Avengers to different realms.