Revenant

A Revenant is a soul of great ambition or power that died before its purpose was fully served, and their spirit inhabits their body or another dead body to carry out their purpose with an indomitable will.

Revenants are supposedly sent back to life by the Gods, with special powers granted to them to carry out their task. Once their purpose is fulfilled, they are released from their unlife and their soul sent to The City of the Dead for final judgement and eternal rest.