Udāyin is a member of band of six monks who are controversial figures in the history of Buddhism. His deeds are not only contained in Vinaya, but also found in Chinese Āgama, Theragāthā, and the literature of Buddha biography, etc. The records of six monks are diverse and their identities are without consent. On the other hand, the compilation of Mūlasarvāstivāda-vinaya was later than other Vinayas and resulted in voluminous. Based on previous materials, Mūlasarvāstivāda-vinaya composed the entire life of Udāyin who was unique among six monks. This article attempts to utilize all the records about Udāyin by category, comparison and analysis, with an eye to show the whole picture of Udāyin and also make some observations on the compilation of Mūlasarvāstivāda-vinaya.
