The Grand Widow

The Splinter of Atiesh was material for the Legendary weapon 'Atiesh, Greatstaff of the Guardian'.

Naturally, the Guardian mentioned here was the Guardian of Tirisfal.

After Karazhan fell, the Kirin Tor Assembly dispatched a whole team of Mages to search the whole tower and collect all the important things. In the end, this staff was taken to Dalaran.

A whole series of unfortunate events had occurred in Dalaran. All those who had encountered Atiesh, even those who had just done some work with the Kirin Tor Mages, had all died strangely. It was like it was a sentient magical weapon. This sentience must have been granted by Sargeras. However, it was no longer the carrier of the Guardian's strength.

After these people died, the Kirin Tor Sixth Assembly made a decision. They thought the best way to deal with this staff was to use some long-lasting magic to seal it up inside a prison.