Saicho, honoured by the posthumous title Dengyo Daishi, is, with his contemporary Kukai, one of the two monks who transformed Japanese Buddhism at the opening of the Heian period. Ordained young and dissatisfied with the corruption of the established Nara schools, he withdrew to Mount Hiei near the new capital, and in 804 travelled to China, on the same embassy as Kukai, where he received transmission in the Tiantai teaching.
Returning, he founded the Japanese Tendai school, centred on the supremacy of the Lotus Sutra and its teaching that all beings possess the capacity for Buddhahood. His great institutional struggle was for the right of Tendai to ordain its own monks under a Mahayana bodhisattva precept platform, independent of the older Nara ordination system, a right granted only after his death, and one that made Mount Hiei the training ground of Japanese Buddhism for centuries. Nearly every major later movement, the Pure Land of Honen and Shinran, the Zen of Dogen, the Nichiren school, was founded by a monk who began on Hiei. Saicho's reform thus seeded, indirectly, almost the whole subsequent history of Buddhism in Japan.