On June 23, 1534, Oda Nobunaga (織田信長, Oda Nobunaga) was born in Owari Province (尾張国, Owari no kuni), in what is now Aichi Prefecture. His father, Oda Nobuhide (織田信秀, Oda Nobuhide), was a deputy shugo (守護, shugo) — a military governor of modest rank in a domain riven by competing factions and powerful neighbors. The child was given the childhood name Kippōshi (吉法師, Kippōshi), an auspicious name meaning something like 'fortunate dharma child.' Nothing about his early years suggested that auspiciousness would look the way it did.

By his teenage years, Kippōshi had shed that name for a crueler one. Owari no Ō-utsuke (尾張の大うつけ, Owari no Ō-utsuke) — the Great Fool of Owari. The Shinchō-Kōki (信長公記, Shinchō-Kōki), a contemporary chronicle of Nobunaga's life, records his behavior in remarkable detail: he walked through town wearing short trousers tied with rope, his robes open at the chest, barefoot. He ate food — including raw things — directly from his sleeve while walking in public, like a street vendor rather than the heir to a domain. He rode horses backwards. He danced in women's clothing at taverns. He ate while standing, called out to strangers, mingled with peasants as though rank meant nothing. For the samurai establishment of Owari, rank meant everything. This boy was an embarrassment.

In 1551, Nobunaga's father Oda Nobuhide died suddenly, leaving the domain to a seventeen-year-old known chiefly for public humiliation. At the funeral — a formal, solemn occasion at which a young lord was expected to demonstrate gravity and fitness for leadership — Nobunaga arrived without proper hakama (袴, hakama), his hair loosely tied. At the moment of the incense offering, he grabbed a fistful of the ritual incense and threw it at the altar, then walked out. The entire samurai establishment of Owari watched.

The man most shaken was Hirate Masahide (平手政秀, Hirate Masahide), Nobunaga's chief tutor and most respected retainer — a senior official who had devoted years to preparing this boy for leadership. In 1553, Masahide committed seppuku (切腹, seppuku). The act is widely believed to have been a form of admonishment, the most extreme remonstration available to a samurai retainer: killing oneself as an appeal to a lord's conscience. Nobunaga, by some accounts, wept. He later built a temple — the Seishu-ji (誓主寺, Seishu-ji) — in Masahide's honor. But the behavior did not change.

Many retainers abandoned Nobunaga in favor of his younger brother Nobuyuki (信行, Nobuyuki), who was polished, conventional, and looked the part. Multiple attempts were made to replace Nobunaga with Nobuyuki — including what amounted to coup attempts within the family. Nobunaga survived them all. He survived his brother's challenges, consolidated the fractious Oda vassal lords, and by the time he was in his mid-twenties had brought all of Owari under his control.

History would eventually reveal what the samurai establishment could not see: the same defiance of convention that horrified the traditionalists was precisely the quality that made Nobunaga so dangerous. He had no attachment to the way things had always been done. He adopted the arquebus (火縄銃, hinawajū) and used it in disciplined volley tactics at the Battle of Nagashino (長篠の戦い, Nagashino no Tatakai) in 1575, breaking Takeda cavalry in a way no one had thought possible. He built Azuchi Castle (安土城, Azuchi-jō) with a stone keep — the first of its kind in Japan — as a statement of power and permanence. He dissolved the Ashikaga Shogunate (足利将軍家, Ashikaga Shōgunke) in 1573 because it stood in his way. He welcomed Jesuit missionaries while the samurai establishment muttered about foreigners. Every instinct that made him Owari no Outsuke became a weapon.

He also chose his own name for what he was. Late in his life, Nobunaga began signing letters with the title 第六天魔王 (Dairokuten Maō) — Demon King of the Sixth Heaven. It was not imposed on him. He chose it. The fool had always known exactly what he was doing.

He was killed on June 21, 1582, at the Honnō-ji (本能寺, Honnō-ji) temple in Kyoto — two days before his 48th birthday. He was 47. The Great Fool of Owari had remade Japan in his own image, and it would never fully revert.