The Ring Of The Servant is a Ring, one of the possible random awards for defeating the Dark Knight.
Double clicking the ring while it is equipped will cause it to instantly heal you as though you'd cast Greater Heal on yourself. The amount of health restored is based on your Magery skill.
This effect has no casting time attached to it and does not effect any non-Spell Channeling items you might have equipped. There is a five minute cooldown time between uses.
The charges on this ring cannot be replenished.