The Ancient Shadowmoon Spirit at the Altar of Shadows in southeast Shadowmoon Valley wants you to recover Gorefiend's Cloak.
Many a cruel act he committed but none so cold as the slaughter of the clerics of Karabor.
After Gul'dan's Horde defeated the draenei of Karabor, the surviving clerics of Karabor were marched out, told that they were to be taken to Hellfire Citadel as prisoners of war.
Gorefiend, not yet a death knight, murdered each and every last one of them in cold blood. They now roam in front of the Black Temple with vengeance in their hearts.
It is the clerics of Karabor that hold the cloak of Gorefiend.