John VIII Palaiologos

John VIII Palaiologos or Palaeologus (; 18 December 1392 – 31 October 1448) was the penultimate Byzantine emperor. Ruling from 1425 to 1448, he attempted, and failed, the reunification of the Orthodox and Catholic churches and prioritized the protection of Constantinople against the Ottoman Empire, he was succeeded by his brother, Constantine XI. Biography John VIII was the eldest son of Manuel II Palaiologos and Helena Dragaš, the daughter of the Serbian prince Constantine Dragaš. He was associated as co-emperor with his father before 1416 and became sole emperor on 1 July 1425, although he had already assumed full power on 19 January 1421. In June 1422, John VIII Palaiologos supervised the defense of Constantinople during a siege by Murad II, but had to accept the loss of Thessalonica, which his brother Andronikos had given to Venice in 1423. To secure protection against the Ottomans, he made two journeys to Italy in 1423 and 1439. During the second journey he visited Pope Eugene IV in Ferrara and consented to the union of the Greek and Roman churches. The union was ratified at the Council of Florence in 1439, which John attended with 700 followers including Patriarch Joseph II of Constantinople and George Gemistos Plethon, a Neoplatonist philosopher influential among the academics of Italy. The union failed due to opposition in Constantinople, but through his prudent conduct towards the Ottoman Empire he succeeded in holding possession of the city. 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.