Photius I is widely regarded as the most powerful and influential church leader of Constantinople subsequent to John Chrysostom's archbishopric around the turn of the fifth century.

In 858, Emperor Michael III (r. 842–867) decided to confine Patriarch Ignatius in order to force him into resignation, and Photius, still a layman, was appointed to replace him.

The chief contemporary authority for the life of Photius is his bitter enemy, Niketas David Paphlagon, the biographer of his rival Ignatius.

[12] Byzantine writers also report that Emperor Michael III (r. 842–867) once angrily called Photius "Khazar-faced", but whether this was a generic insult or a reference to his ethnicity is unclear.

The famous library he possessed attests to his enormous erudition (theology, history, grammar, philosophy, law, the natural sciences, and medicine).

[19] Photius's ecclesiastical career took off spectacularly after Caesar Bardas and his nephew, the youthful Emperor Michael III, put an end to the administration of the regent Theodora and the Logothetes tou dromou Theoktistos in 856.

In 858, Bardas found himself opposed by the then Patriarch Ignatius of Constantinople, who refused to admit him into Hagia Sophia, since it was believed that he was having an affair with his widowed daughter-in-law.

In response, Bardas and Michael engineered Ignatius's confinement and removal on the charge of treason, thus leaving the patriarchal throne empty.

The latter's confinement and removal without a formal ecclesiastical trial meant that Photius's election was uncanonical, and eventually Pope Nicholas I sought to involve himself in determining the legitimacy of the succession.

[24] The situation was additionally complicated by the question of papal authority over the entire Church and by disputed jurisdiction over newly converted Bulgaria.

[25] This state of affairs changed with the murder of Photius's patron Bardas in 866 and of Emperor Michael III in 867, by his colleague Basil I, who now usurped the throne.

From surviving letters of Photius I written during his exile at the Skepi monastery, it appears that the ex-patriarch brought pressure to bear on the Byzantine emperor to restore him.

Ignatius' biographer argues that Photius forged a document relating to the genealogy and rule of Basil I's family, and had it placed in the imperial library where a friend of his was a librarian.

Pope Adrian III chose a policy of appeasement and sent between 884 and 885 bishop Theodosius of Oria to transmit notice of his election and a synodal letter to Photius about faith and the Filioque.

He sought to bridge the confessional differences between the Greek Orthodox and Armenian churches on two separate occasions, once in 862 and again in 877, but his efforts ultimately proved unsuccessful.

Warren Treadgold believes that this time the evidence points to a plot on behalf of Leo VI, who became emperor, and deposed Photius I, although the latter had been his tutor.

Latin sources confirm that while he did not die in a state of complete excommunication, having been reinstated by a council which was approved by Pope John VIII, his ecclesiastical career was viewed in utter disgrace by Catholic authorities and many of his theological opinions were condemned posthumously.

His name features in a manuscript of the Typicon of the Great Church of Constantinople dated to the middle of the tenth century, where he is referred to a saint with a day of commemoration of February 6.

One of the most learned men of his age, and revered – even by some of his opponents and detractors – as the most prolific theologian of his time, he has earned his fame due to his part in ecclesiastical conflicts, and also for his intellect and literary works.

[45] Adrian Fortescue regards him as "one of the most wonderful men of all the Middle Ages", and stresses that "had [he] not given his name to the great schism, he would always be remembered as the greatest scholar of his time".

That Ignatius was the rightful patriarch as long as he lived, and Photius an intruder, cannot be denied by any one who does not conceive the Church as merely the slave of a civil government.

[47] The most important of the works of Photius I is his Bibliotheca or Myriobiblon, a collection of extracts and abridgements of 280 volumes of previous authors (usually cited as Codices), the originals of which are now to a great extent lost.

For a long time, the only manuscripts of the Lexicon were the Codex Galeanus, which passed into the library of Trinity College, Cambridge[17] and Berolinensis grace., 22 October, both of which were incomplete.

But in 1959, Linos Politis of the University of Thessaloniki discovered a complete manuscript, codex Zavordensis 95, in the Zavorda Monastery (Greek: Ζάβορδα) in Grevena, Greece, where it still resides.

[51] His most important theological work is the Amphilochia, a collection of some 300 questions and answers on difficult points in Scripture, addressed to Amphilochius, archbishop of Cyzicus.

[60] ^ d: Toby Bromige notes that "Shirinian identifies many influential Byzantines in the mid-ninth century, such as Photios [...] as Armenian in origin, but these claims have been challenged".

[61] There is a tendency amongst certain Byzantinists to propose an "Armenian" ancestry for certain Byzantine individuals and/or families with an obscure heritage as a "convenient solution",[62] even if the evidence is flimsy, non-existent or completely fictional.