Photios I (Greek: Φώτιος Phōtios; c. 810 – c.893),a[›] also spelled Photius (/ˈfoʊʃəs/) or Fotios, was the Ecumenical Patriarch of Constantinople from 858 to 867 and from 877 to 886;[1] He is recognized in the Eastern Orthodox Church as St. Photios the Great.

Photios is widely regarded as the most powerful and influential Patriarch of Constantinople since John Chrysostom, and as the most important intellectual of his time, "the leading light of the ninth-century renaissance". He was a central figure in both the conversion of the Slavs to Christianity and the Photian schism.

Photios was a well-educated man from a noble Constantinopolitan family. Photius's great uncle was a previous Patriarch of Constantinople, Tarasius. He intended to be a monk, but chose to be a scholar and statesman instead. In 858, Emperor Michael III (r. 842–867) deposed Patriarch Ignatius of Constantinople, and Photios, still a layman, was appointed in his place. Amid power struggles between the pope and the Byzantine emperor, Ignatius was reinstated.

Photios resumed the position when Ignatius died (877), by order of the Byzantine emperor.

The new pope, John VIII, approved Photios's reinstatement.[6] Catholics regard a Fourth Council of Constantinople (Roman Catholic) as anathematizing Photios as legitimate. Eastern Orthodox regard a second council named the Fourth Council of Constantinople (Eastern Orthodox), reversing the first, as legitimate. The contested Ecumenical Councils mark the end of unity represented by the first seven Ecumenical Councils.

Concerning statements in the sacred teachings which state that as the Son is begotten of the Father alone, so likewise the proper theology concerning the Holy Spirit is that He proceeds from one and the same cause; and also concerning the saying that because He is of one essence with the Son, He therefore proceeds from Him as well.