Saint Demetrios of Thessaloniki (Greek: Άγιος Δημήτριος της Θεσσαλονίκης) is a Christian martyr of the early 4th century AD.
During the Middle Ages, he came to be revered as one of the most important Orthodox military saints, often paired with Saint George. His feast day is 26 October for Eastern Orthodox Christians following the Gregorian calendar and 8 November for those following the Julian calendar. In the Roman Catholic church he is most commonly called "Demetrios of Sermium" and his memorial falls on 8 October.
The spelling "Demetrius" is a romanization of the ancient Greek pronunciation; the Byzantine and Modern Greek pronunciation is romanized as Dimitrios or Demetrios. See Demetrios for more on the etymology of the name.
In Russian, he is called Димитрий Солунский ([dimitri solunski] 'Dimitri of Saloniki') and was a patron saint of the Rurik dynasty from the late 11th century on. Izyaslav I of Kiev (whose Christian name was Dimitry) founded the first East Slavic monastery dedicated to this saint. The name Dimitry is in common use.
The Bulgarian Orthodox Church reveres St. Demetrios on 26 October as Димитровден (Dimitrovden).
The Romanian Orthodox Church revers St. Demetrios on 26 October as Sf. Dumitru.
The Serbian Orthodox Church reveres St. Demetrios as Димитрије, having a feast of Mitrovdan on 8 November.
The Macedonian Orthodox Church reveres St. Demetrios on 8 November as Митровден (Mitrovden)
He is known among Albanian-speakers in Kosovo as Shmitri, and in Albania as Shën Dhimitri.
He is known in Lebanon as Mar Dimitri or Mitri for short, which is a common name among Christian Lebanese.
He is known in the Coptic Church as "St. Demetrios of Thessalonica". He is venerated in the Coptic Church on 8 November.
The earliest written accounts of his life were compiled in the 9th century, although there are earlier images of him, and the 7th-century Miracles of Saint Demetrios collection. According to these early accounts, Demetrios was born to pious Christian parents in Thessaloniki, Illyricum in 270.The biographies have Demetrios as a young man of senatorial family who was run through with spears in around 306 AD in Thessaloniki, during the Christian persecutions of Diocletian and Galerian, which matches his depiction in the 7th century mosaics.