Life
John VIII Palaiologos was the eldest son of Manuel II Palaiologos and Helena Dragaš, the daughter of the Serbian prince Constantine Dragaš. He had been associated as co-emperor with his father before 1416 and became sole emperor in 1425. He was married three times, first to Anna, daughter of Grand Prince Basil I of Moscow (1389–1425) in 1414, then to Sophia of Montferrat in 1421, and the last time to Maria, daughter of the emperor of Trebizond, in 1435. None of the marriages produced any children.
In June 1422, John VIII Palaiologos had supervised the defense of Constantinople during a siege by Sultan Murad II, but had to accept the loss of Thessalonica to the Ottoman Turks in 1430. To secure protection against the Ottomans, he visited Pope Eugene IV and consented to the union of the Greek and Roman churches, which was ratified at the Council of Florence in 1439. He was accompanied by the Patriarch of Constantinople Joseph II, and by George Gemistos Plethon, a Neoplatonist philosopher who was very influential among the academics of Italy and influenced the nascent western European Renaissance. The proposed church union failed due to opposition by his own people, who refused to submit to the Pope, but by his prudent conduct towards the Ottoman Empire he succeeded in holding possession of Constantinople.
John VIII Palaiologos named his brother Constantine XI, who had served as regent in Constantinople in 1437–1439, as his successor. Despite the machinations of his younger brother Demetrios Palaiologos his mother Helena was able to secure Constantine XI's succession in 1448.
