Deathless Guardians, also known as undying warriors and commonly referred to as Ancient warriors, were warriors that offered their bodies and souls to the Priestesses and in turn were blessed with immortality. The pact passed on through the priestesses' bloodline and would end when there was no heir to pass on to.
Mark of the Deathless Pact
These warriors share the same mark on their masks as the priestesses - signifying their pact. As they are undying, the Ancients were a formidable foe against the King of the First Age when they first arrived on the continent. This was, at least, until the settlers learned that the warriors could be subdued using magic.[1]
Despite there being historically an army of them, there have only been two Deathless Guardians shown in the game: