According to legend, he was a legionary in the Roman army who suffered martyrdom by immolation at Amasea in Galatian Pontus (modern Amasya, Turkey) during the Great Persecution under Diocletian in the early 4th century.

Venerated by the late 4th century, he became a prominent warrior saint during the Middle Ages, attracted a great deal of additional legends including accounts of battle against dragons, and was often confused with (or was the original source of) the similar Theodore Stratelates of Heraclea.

Theodore is the English form of the Latin masculine given name Theodorus from Ancient Greek Theódōros (Θεόδωρος) from Theós (Θεός, "God") + dō̂ron (δῶρον, "gift").

[10] (Nilles argued that this epithet was a later mistake and that, rather than being a recruit, Theodore's name had originally referenced his service in the Cohors Tyronum.

[1] Christianity was still illegal and Galerius, prior to his 311 Edict of Toleration at Serdica, enforced his co-emperor Diocletian's Great Persecution.

When the soldiers of Theodore's cohort were obliged to perform pagan sacrifice at Amasea in Galatian Pontus (modern Amasya, Turkey, about 30 miles or 48 kilometres south of the Black Coast at Sinop), he refused and recounted a confession of faith in the divinity of Jesus Christ.

[1] Theodore then burned the city's temple of Magna Mater (Cybele), whereupon he was again arrested, tortured, and martyred by immolation.

The earliest image of St Theodore as a horseman (named in Latin) is from Vinica, North Macedonia and, if genuine, dates to the 6th or 7th century.

The "Christianisation" of the Thracian horseman iconography can be traced to the Cappadocian cave churches of Göreme, where frescoes of the 10th century show military saints on horseback confronting serpents with one, two or three heads.

One of the earliest examples is from the church known as Mavrucan 3 (Güzelöz, Yeşilhisar [tr]), generally dated to the 10th century,[21][22] which portrays two "sacred riders" confronting a two serpents twined around a tree, in a striking parallel to the Dioskuroi stela, except that the riders are now attacking the snake in the "tree of life" instead of a boar.

[23] A poorly preserved wall-painting at the Yılanlı Kilise [tr] ("Snake Church") that depicts the two saints Theodore and George attacking a dragon has been tentatively dated to the 10th century,[24] or alternatively even to the mid-9th.

[25] A similar example, but showing three equestrian saints, Demetrius, Theodore and George, is from the "Zoodochos Pigi" chapel in central Macedonia in Greece, in the prefecture of Kilkis, near the modern village of Kolchida, dated to the 9th or 10th century.

[37] The veneration of St Theodore is attested by the late 4th century, when Gregory of Nyssa preached an encomium or homily[4] in his honor at his sanctuary[17][38][39] in the winter of 381.

From at least the 9th century (and possibly much earlier), Euchaita housed the relics of the saint and became an important place of pilgrimage, to the point it was also known as Theodoropolis.

Gregory of Nyssa said nothing about St Theodore's life beyond the basic legend as given above, but he told how he could influence the lives of his hearers and specifically mentioned that he could intervene in battles.

[1] Chartres Cathedral in France has a 13th-century stained glass window with 38 panels depicting Theodore's life,[1] but his cult did not become common beyond Italy.

At the end of the Presanctified Liturgy on Friday evening (since, liturgically, the day begins at sunset) a special canon to St. Theodore, composed by St. John of Damascus, is chanted.

Then the priest blesses kolyva (boiled wheat with honey and raisins) which is distributed to the faithful in commemoration of the following miracle worked by St. Theodore on the First Saturday of Great Lent: Fifty years after the death of St Theodore, the emperor Julian the Apostate (361-363) commanded the governor of Constantinople during the first week of Great Lent to sprinkle all the food provisions in the marketplace with the blood offered to pagan idols, knowing that the people would be hungry after the strict fasting of the first week.

St Theodore appeared in a dream to the Archbishop of Constantinople, Eudoxius, ordering him to inform all the Christians that no one should buy anything at the market, but rather to boil the wheat they had at home and eat it sweetened with honey.

After the service, the kolyva is distributed to all who are present and, after Holy Communion and the antidoron, is the first food eaten after the strict fasting of the first week.

[51] However, Demus later noted that none of the 12th-century mosaics which show St Theodore mentions more than his name and that he may have become the patron of the city before the two saints were distinguished.