Shuten-dōji

Shuten dōji (Japanese: 酒呑童子 or しゅてんどうじ, meaning "little drunkard") was the king of Oni, and a local tyrant from Mt Oeyama before he was slain by Minamoto no Yorimitsu in Japanese mythology.

Myths & Legends
There are three monsters who are considered the greatest and most evil yokai in all of Japanese folklore: the ghost of Emperor Sutoku, the nine-tailed kitsune Tamamo no Mae, and the dreaded king of the oni, Shuten dōji.

Birth
Shuten dōji was not born an oni. There are many stories about how he came to be, but most of them say that he was originally a human boy who was born over a thousand years ago either in present-day Shiga or Toyama. His mother was a human woman and his father was the great dragon Yamato-no-Orochi. How he changed from boy to demon varies greatly from story to story, but the one popular version goes like this: There was a young boy who was supernaturally strong and abnormally intelligent for his age. Everyone around him constantly called him a demon child due to his incredible strength and wit, and he gradually became terribly anti-social and resentful of others.

At age six, even his own mother abandoned him. Orphaned, he became an apprentice priest at Mt. Hiei in Kyoto. Naturally, he was the strongest and smartest of the young acolytes, and he grew resentful of them as well. He slacked off on his studies as a result and got into fights. He also fell into drinking, which was forbidden to monks; however he could out-drink anyone and everyone who was willing to sit down and drink against him. Because of his fondness for alcohol, he became known as Shuten dōji, "the little drunkard."

Transformation
One night there was a festival at the temple, and Shuten dōji showed up very drunk. He put on an oni mask and went around playing pranks on his fellow priests, jumping out from the darkness to scare them and such. At the end of the night, he tried to take off his mask but found he couldn't — to his horror, it had fused to his body! Ashamed, scared, and scolded by his masters for being drunk, he fled into the mountains where he would no longer have to interact with other humans, whom he saw as weak, foolish, and hypocritical. He lived there on the outskirts of Kyoto for many years, stealing food and alcohol from villagers, and drinking vast quantities of alcohol. His banditry eventually attracted groups of thieves and criminals, who stuck with him loyally and became the foundation for his gang.

King of Demons
Living in exile, Shuten dōji grew in power and knowledge. He mastered strange, dark magic, and taught it to his thugs. He met another demon child like him, named Ibaraki dōji, who became his chief servant. Over time, the young man and his gang gradually transformed into oni, and eventually he had a whole clan of oni and yokai thugs who prowled the highways, terrorizing the people of Kyoto in a drunken rage. He and his gang eventually settled on Mount Ōe, where, in a dark castle, he plotted to conquer the capital and rule as emperor.

Shuten dōji and his gang rampaged through Kyoto, capturing noble virgins, drinking their blood and eating their organs raw. Finally, a band of heroes led by the legendary warrior Minamoto no Yorimitsu assaulted Shuten dōji's palace, and with the help of some magical poison, were able to assault the oni band during a bout of heavy drinking. They cut off the drunken Shuten dōji's head, but even after cutting it off, the head continued to bite at Minamoto no Yorimitsu.

Because the head belonged to an oni and was unholy, it was buried it outside of the city limits, at a mountain pass called Oinosaka. The cup and bottle of poison that Minamoto no Yorimitsu used are said to be kept at Nariai-ji temple in Kyoto.