Every Rinzai Zen lineage in Japan today runs back through the heirs of Hakuin Ekaku, and the sequence of kōan, the riddling cases on which a Rinzai monk is examined, was put in order by his successors. When he began, the school had lost its rich patrons and was turning to lay people for support, and the Ōbaku school, newly arrived from China, was winning monks with a stricter communal training. Hakuin spent fifty years as priest of Shōin-ji, a small temple in Hara, a post town on the Tōkaidō road at the foot of Mount Fuji, and made it a place monks crossed the country to reach.
Most of what is known of his path comes from his own telling, above all Itsumadegusa ("Wild Ivy"), the autobiography he wrote in 1765, and from the chronological biography by his disciple Tōrei Enji. As a child, he writes, a Nichiren preacher's sermon on the hot hells terrified him, and he became a monk at fifteen to escape them. At nineteen he read that Yantou, a great Chinese master, had been murdered by bandits, and he despaired of what Zen could do. At twenty-four, after seven days of sitting shut away at Eigen-ji, he heard a temple bell and took himself to be awakened. Shōju Rōjin (Dōkyō Etan), a hermit teacher with whom he then studied for eight months, mocked the claim and gave him harder cases. Hakuin pressed on so hard that his health broke. In Idle Talk on a Night Boat, printed in 1757 and in print ever since, he told how a hermit in the hills outside Kyoto taught him the breathing that cured him.
From his mid-twenties, he says, one sentence troubled him: that sages and holy monks who lack bodhicitta, the mind set on awakening, all fall among the demons. In his early forties, reading the Lotus Sutra, he came to the chapter of parables and understood the sentence at last. Bodhicitta, he concluded, is doing good: teaching others and benefiting them. This is the claim at the centre of his Zen. Awakening is not a calm to rest in; the real work is the practice that comes after it, and it is done for others.
Everything he taught follows from that. He wanted beginners driven into what he called the great doubt, holding a single question until it gave way, and for them he devised his own first case, the sound of one hand, which he judged far better than the traditional first kōan. He attacked teachers who equated a quiet empty mind with enlightenment. In 1749 he lectured on the sermons of Daitō, the fourteenth-century founder of Daitoku-ji, and his commentary, Kaian kokugo, turns Daitō's hardest words against monks who sat all day and called the calm awakening.
He spent his last fifteen years writing, much of it in plain Japanese and popular verse that commoners could read, and he took up painting at almost sixty. His ink portraits of Bodhidharma and his calligraphy, made for lay people who often could not read, now hang in museums. He died at Shōin-ji, in the village where he was born, in 1769, at eighty-three.
His closest disciple, Tōrei, received his robe, but today's lineages descend through Gasan Jitō and Gasan's students Inzan Ien and Takuju Kosen, and scholars doubt that Gasan was formally Hakuin's heir at all. Hakuin himself never received a formal transmission from Shōju or anyone else. All fourteen branches of the Rinzai school count him as their restorer, and their monks recite his Zazen wasan, a hymn in praise of sitting, when they sit.