Helm of the Fallen Defender

Helm of the Fallen Defender is a tier 4 armor token. It can be exchanged at Asuur at Shattrath's Aldor Rise or Arodis Sunblade on the Scryer's Tier for the following items:

It can also be exchanged at Karynna at the Isle of Quel'Danas for the following Season 1 PvP items:

Source
This item drops from Prince Malchezzar in Karazhan.