Complex sentence: Theodore was not the same person as Theodore of Stoudious, that man had lived two centuries before, and was also a monk at the same monastery who was persecuted for his devotion to religious icons or images during the Iconoclastic period.
Split into simpler sentences: Theodore was not the same person as Theodore of Stoudious, however. That man had lived two centuries before, and was also a monk at the same monastery who was persecuted for his devotion to religious icons or images during the Iconoclastic period.