A Goryo is a the ghost of an ancient warrior and noble who died horrible, agonizing deaths and returned to haunt their enemies as dreadful ghosts of vengeance, similar to the Onryo.
They bring ruin to those that wronged them in life via a variety of curses and calamities such as fires, wars, plagues, droughts, floods, storms, the deaths of imperial family members and other disasters.
Goryo cannot be killed and thus the only way to end their wrath was to transform them into peaceful, benevolent spirits with the help of priests and onmyoji, through the religion known as goryo shinko, the "religion of ghosts".