Zois is a magical ring, crafted by Hephaistos and stolen by Odysseus.This ring has great healing-powers and is the reason that he managed to survive as much as he have. Killing a person wielding this ring is more or less impossible. Ares, among others, tried to take it from Odysseus several times. Zois has 7 charges, which can be used for several things as you can see in the following document. Zois regains 1d6 charges every dawn

Healing factor
The wielder of this ring get's 20 hp in the beginning of it's turn, every turn. Besides this effect the wielder can also expend three charges to regain all it's hitpoints. Once this ability is used it can't be used for 24 hours again. Doing this takes one action

Protection from harm
The wielder of Zois can expend one of it's charges in order to become imune to one type of damage for 24 hours. Doing this takes one bonus action, and the wielder can't be imune to more than one damage-type due to this effect at a time.

Notes: by a Cleric, Ranger, Pladin or Sorcerer