Saicho, posthumously Dengyo Daishi, is a priest in Heian Era, who was born in current Ohtsu-City, Shiga Pref. He received the Buddhist Commandments at Kaidan-In in Todai-ji Temple in Nara. But he despaired at corruption of the religious world in Nara of those days, and he ascended to Mt. Hiei in Kyoto to set up Ichijo-Shikan-In, which is currently the Enryaku-ji Temple.
After that, he journeyed to China to study the Tientai(J., Tendai) school. Two years later, he returned from China and preached Tendai Buddhism in Enryaku-ji Temple.
Tendai is a comprehensive sect, which contains esotericism, Zen, Nembutsu (invocation to Amida Buddha) and so on. Tendai Sect greatly influenced the Japanese thought and culture as it fostered the founders of the "new Kamakura Buddhist sects", including Jodo Sect, Jodo-shin Sect, Nichiren Sect, Rinzai Sect and Soto Sect.