Athanasius I was a 9th-century bishop who led the diocese of Naples from 850 until his death in 872. Born in Naples to Sergius I, he was consecrated by Pope Leo IV at a young age. Throughout his tenure, he maintained close ties with both the papacy and imperial courts, serving as a papal legate. Known for his ascetic lifestyle, he focused heavily on clerical training and the establishment of religious institutions within his territory.