Ring of the Fallen God

The Ring of the Fallen God is a caster ring with great stats and bonuses for a caster.

Source
The Ring of the Fallen God is a quest reward from the quest which starts with Caelastrasz in the Temple of Ahn'Qiraj in Silithus. To complete the quest, you must turn in one to Anachronos. This item drops from C'thun, the last boss of Ahn'Qiraj.