Rengō 蓮剛 (dates unknown, fl. probably mid-Heian to early-Kamakura, c. 850–1200) was a Japanese Tendai school missionary who is otherwise unattested in standard biographical sources. He identifies himself in the colophon of his single surviving work, KR6t0067 Dìngzōng lùn, as “the Śākya-clan monk Rengō, a disciple of the Tendai school” (天台門徒蓮剛), and reports that the work originated during a missionary preaching circuit in the Saikaidō 西海道 — the Kyushu region of medieval Japan. The work is a structured 12-chapter doctrinal apology for the Tendai school against the rival Buddhist schools of his day (Sānlùn, Faxiang, Huayan, Risshū, and Shingon).
No CBDB or DILA Authority record currently locates this Rengō. He should be distinguished from the Sōtō Zen monk Rengō and from various Hossō-school namesakes of the period.