Also known by its Japanese name Kegon (j), the Hua-yen (wg) or "Flower Ornament" Buddhist Order is named after its primary text the Avataṃsaka Sūtra. The Avataṃsaka Sūtra (s), Dafangguangfo huayan jing (ch), Kegonkyō (j) one of the "Vaipulya" (expansive) Mahāyana Buddhist scriptures. Vaipulya refers not only to its length but also to its profundity. The Hua-yen was first referred to as a Sect of its own right by the Fifth Patriarch Tsung-mi (780-841), thus the preceding four patriarchs were named posthumously. Some later scholar consider Fazan to be the founder of the Order but the Hua-yen Order is generally considered to have been "founded" by Du-shun (wg), Dojun (j) in about 600 CE.
Du-shun (557-640) who is said to be an incarnation of the Bodhisattva Mañjuśri started practicing Ch'an under the master Seng-chen at the age of eighteen. Thereafter he gained a reputation for his supernatural and healing abilities. Having advised the Emperor T'ai-tsung he was awarded honorary title of "the Venerable One of the Imperial Heart". Du-shun developed the "Five Levels of Teaching" and "Ten Profound Gates" which are the basis of the order's philosophical view.
The "Five Levels of Teaching" is a refinement of the Tien-t'ai classification scheme and alterately categorizes the Sūtras as:
Chih-yen/Zhiyan (602-668) the Second Patriarch had, even as a child, an inclination for Buddhism. He studied numerous Scriptures under the She-lun and Wei-chih scholars Fa-ch'ang (567-645) and Seng-pien (568-642) respectively, but finally decided to concentrate on the Avataṃsaka Sūtra. Writing many commentaries he set up a refined theoretical foundation for the Hua-yen including the the introduction of the doctrine of the interpenetration and mutual identification of all phenomena.
Fazan refined the refined further the Hua-yen doctrinal and theoretical system and with his eloquence and political astuteness, he brought the order to prominence during the reign of Empress Wu Zetian (625-705) as well as during the reigns of Emperor Ruizong.
Perhaps the Order's success made it prone to rigidity and narrow-mindedness. After Fazan's death one of his scholarly pupils, Hui-yŁan, seem destined to become Fazan's sucessor, however that his doctrinal views differed from the orthodox interpretation led to his excommunication.
Similarly, the lay scholar Li T'ung-hsuan/Li Tongxuan (647-740) also developed and published non-orthodox interpretations of the Hua-yen scripture. His texts were popular among intellectuals and, especially a few decades later, with Linchi Ch'an practitioners but among the Hua-yen establichment however he was branded as heterodoxical by the Chinese Hua-yen as well as the later Japanese Kegon othodoxy.
Filling the long gap left by Huiyuan's excommunication, Chengguan (738-839), the fourth the Hua-yen Patriarch, was known for his comprehensive knowlege of Buddhism, Sanskrit, Chinese classics and arts. Chengguan was highly regarded to the exent to which he was the Imperial Master of seven sucessive Emperors.
The fifth Patriarch Tsung-mi (780-841) had previously studied Konfucianism as well as Ch'an before meeting Chuanguan. During his time the Hua-yen widely influenced particularly Rinzai Ch'an Buddhism.
After Tsung-mi's death, the order suffered tremendously during the reign of Emperor Wu Zong (841-847). During this time Chinese Buddhist monasteries were systematically destroyed and Buddhist texts burned. Fortunately, the Hua-yen order had already been introduced to Silla (Korea) by the Chinese monk Dao Xuan (py), Tao Hsuan (wg), Dōsen (j) (702-760) in 736 where it became known as the Kwa Om order and to Japan by the monk Shinshō (j) (xx-742) in 740 (as well as by direct contact with the Indian monk Bodhisena (704-760)) and became known as the Kegon order.