Breastplate of the Lost Protector

Breastplate of the Lost Protector is a tier 7 armor token. It can be exchanged in Dalaran for the following items:
 * Valorous Dreadnaught Battleplate
 * Valorous Dreadnaught Breastplate
 * Valorous Cryptstalker Tunic
 * Valorous Earthshatter Chestguard
 * Valorous Earthshatter Hauberk
 * Valorous Earthshatter Tunic

Source
This item can be found inside the Four Horsemen Chest after defeating the Four Horsemen in the 25-man version of Naxxramas. It can also drop from Gluth.