Breastplate of the Lost Conqueror

Breastplate of the Lost Conqueror is a tier 7 armor token. It can be exchanged in Dalaran for the following items:
 * Valorous Redemption Breastplate
 * Valorous Redemption Chestpiece
 * Valorous Redemption Tunic
 * Valorous Robe of Faith
 * Valorous Raiments of Faith
 * Valorous Plagueheart Robe

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.