The Ancient Shadowmoon Spirit at the Altar of Shadows in southeast Shadowmoon Valley wants you to recover Gorefiend's Armor.
In life, Gorefiend was a monster, but in death, Gorefiend was an unmitigated terror.
To the southeast you will find Netherwing Ledge. What was once part of the mainland of Shadowmoon is now a floating island in the sky.
Vhel'kur, spawn of Deathwing, once called it his home, but now knows it as his grave. He flies an endless circle above the island, seething at his defeat to Gorefiend.
If you are to recover the Gorefiend's armor, it is Vhel'kur that you must defeat.