Sutoku Tennō is one of the three most famous yōkai to ever haunt Japan. After he died, he transformed—some say into a terrible onryō, some say into a great tengu—and inflicted his wrath upon the imperial court at Kyōto. Along with Sugawara no Michizane and Taira no Masakado, he is one of the legendary Nihon San Dai Onryō—the Three Great Onryō of Japan.