Heian period Japanese monk and the founder of the Shingon (‘Mantra’ or ‘True Word’) school of Buddhism. Born into a prominent family in Shikoku, he was sent to study Confucianism.poetry, and culture in Nagaoka and later at the imperial university, with hopes for attaining a high governmental position. However, he abruptly abandoned his studies midway and entered the Buddhist order. From the beginning Kūkai was attracted to esoteric practice, and devoted himself to chanting mantras and studying esoteric scriptures. After a period of living in the mountains as a self-ordained monk, he decided to go to China to further his knowledge. Sailing with a diplomatic delegation in 804, he went to the capital Ch'ang-an and met the esoteric master Hui-kuo (746–805), a man widely recognized as the seventh patriarch of the esoteric school (see esoteric Buddhism) of China. According to legend, Hui-kuo, upon seeing Kūkai enter the temple, immediately saw in him the disciple for whom he had been waiting all his life. He personally took Kūkai through many stages of esoteric initiation (abhiṣeka) and training in the brief time remaining in his life, and Kūkai returned to Japan in 806 wearing the mantle of the eighth patriarch. At first, Kūkai had difficulty establishing himself. Saichō (767–822), who had sailed to China in the same fleet and later was to found the Tendai school, had returned to Japan first bringing his own training in esoteric rituals to the court, and so Kūkai appeared redundant at first. However, it became apparent that his training had been far more extensive and specialized than Saichō's, and after three years he began to rise to prominence and ultimately overshadowed Saichō as Japan's premier esoteric master.
Kūkai is remembered as one of Japan's greatest calligraphers, and it was this that finally brought him to the attention of the court, since Emperor Saga valued this art and is himself considered a master of it. After he gave Kūkai many commissions to inscribe court documents, the two became friendly and Kūkai successfully petitioned him for permission to construct a monastery complex (vihāra) on Mt. Kōya to serve as an exclusive centre for esoteric training. Construction on this site began in 819. Although much work was done during his lifetime, the imperial court kept Kūkai very busy making inscriptions, performing rituals for the protection and peace of the nation, and renovating other temples. This, combined with the remoteness of Mt. Kōya, prevented Kūkai from seeing the completion of this project. The next emperor Junna gave Kūkai the task of completing the Tōji.or Eastern Temple, in the capital city, in return for which he promised to make it an exclusive venue for esoteric practice in which Kūkai would have charge of 50 monks. Perhaps reflecting on the benefits of his own early education, Kūkai made this temple the site of a ‘School of Arts and Sciences’, which accepted students from all walks of life regardless of ability to pay and offered a complete curriculum in both Buddhist and secular subjects. In 847, however, the burden of maintaining the school became too great, and the Tōji sold it off. Esoteric Buddhism was still new, even in China, during Kūkai's lifetime, and his many writings, as well as his work in cataloguing scriptures and ritual texts, put the school on a firm intellectual footing by the time of his death.