Theophanes was the orphan son of a Byzantine provincial governor, so Emperor Constantine V Copronymus raised him at court. Theo got married at age twelve, but persuaded his wife to live in chastity. By fourteen he was probably bitterly regretting this, but he slept in the bed he had made (all alone) and when they came of age, they separated to live chastely. She entered a convent; he entered a monastery, and later founded two other monasteries.
He wrote the Chronograph, which one source dismisses as "a sort of abstract of history from 284 to 813." In spite of its inclination toward atheism, The Great Soviet Encyclopedia is able to muster a little more enthusiasm for Theophanes' Chronograph, noting that it is "the only continuous history of Byzantium and surrounding countries for the years 769 to 813." Many of the sources on which Theophanes drew are now lost, so his lengthy excerpts from these are also valuable.
Theophanes had attended the Second Great Council of Nicea in 787. While there, he signed a statement upholding the veneration of icons. Emperor Leo V (called the Armenian) came to the throne in Constantinople and summoned Theophanes to the capital to recant this doctrine. He refused, suffered two years of brutality in prison, and then was exiled to the island of Samothrace, where he lasted only seventeen days.