Sutoku

was the 75th emperor of Japan, according to the traditional order of succession. He is also called Sanuki-Inn,because he lived in Sanuki (Kagawa) in the later part of his life. Although, officially, he was a child of Toba-Tennno, actually it is said that is not true.
Hogen no Ran.
He struggled with Goshirakawa-Tenno (his brother) for political leadership. This political battle is called Hogen no Ran. He was defeated and was banished to Sanuki.
Legends.
After Sotoku's abdication and exile, he devoted himself to a monastic life. He copied numerous scriptures and offered them to the court. Fearing that the scriptures were cursed, the court refused to accept them. Snubbed, Sotoku was said to have resented the court and, upon his death, became an onryō. Everything from the fall in fortune of the Imperial court, the rise of the samurai powers, droughts and internal unrests were blamed on his haunting.
Other legends say he changed into an Ootengu (greater tengu). Along with nurarihyon, the nine-tailed kitsune Tamamo-no-Mae and the oni Shuten-dōji, they are often called the four greatest yōkai of Japan.