Kōjō 光定 (779–858), posthumously titled Bettō Daishi 別當大師 (“Great Master of the Cloister-Office”), was Saichō’s eldest direct disciple (最澄) and the principal administrator of the Hiei-zan Mahāyāna ordination platform following its imperial establishment in 822. Born in Iyo Province (modern Ehime), he entered Mt. Hiei in his youth and became Saichō’s senior disciple, older than both Gishin (義眞) and Ennin (圓仁). He held the formal title Knower-of-Affairs of the Enryaku-ji Precept-Platform Cloister (延暦寺戒壇院知事) and the Transmission-of-the-Lamp Dharma-Master rank (傳燈法師位), and was the principal officer of the kaidan establishment.
Kōjō played a major role in the institutional struggle for the Mahāyāna kaidan: he was the courier and intermediary between Saichō and the imperial court during the Sōgō dispute of 819–822, and his memorials are preserved as supplementary documents alongside Saichō’s own. After Saichō’s death in 822, Kōjō was a key witness to the imperial granting of the kaidan (one week after Saichō’s death) and supervised the first ordinations on the platform.
His major work KR6t0077 Chuánshù yīxīn jiè wén (composed during the Tenchō or Jōwa era) is the principal historical-doctrinal memoir of the foundational generation of Japanese Tendai. The work narrates Saichō’s life, the institutional struggle for the kaidan, and the doctrinal foundation of the “One-Mind Precepts” (yīxīn jiè 一心戒) — Saichō’s term for the Mahāyāna bodhisattva precepts as institutionalized on Mt. Hiei. The work is the most important Tendai-insider biographical source on Saichō and the institutional history of the precept platform.
Within the Kanripo corpus his preserved work is KR6t0077 Chuánshù yīxīn jiè wén.