Leggings of the Forgotten Vanquisher

Leggings of the Forgotten Vanquisher is a tier 6 armor token. It can be exchanged at Tydormu at the Battle for Mount Hyjal entrance for the following items:

It can also be exchanged at Soryn at the Isle of Quel'Danas for the following Season 2 PvP items:

Source
This item drops from the Illidari Council in the Black Temple.