Bessarion was perhaps the greatest Greek scholar of the early 15th century. His education in Constantinople was supplemented by study under the Neoplatonist Gemistus Pletho (1355?-1452?) in the Peloponnese. This was significant as he later joined Pleitho in trying to heal the schism of the Eastern and Western churches and in leading the revival of Greek learning.
His birth year is given as 1389, 1395, and 1403. When he joined the Order of St. Basil he took the name of the Egyptian anchorite Bessarion. His friendship with the penultimate Byzantine emperor, John VIII Palaeologus (1392-1448) is shown by Bessarion’s arrangement of John’s third marriage, to Maria of Trebizond in 1427. After John named him Archbishop of Nicaea in 1437, Bessarion, having reversed his opposition to a union of the churches, accompanied the emperor, along with Pleitho and others, to councils at Ferrara (1438) and Florence (1445), in hopes of repairing the schism and gaining reinforcements against the encroaching Ottoman Empire. Pleitho introduced Plato into church theology in hopes of finding commonalty and increasing the speculative nature of theology, but though John agreed to a reconciliation, he was opposed back in Constantinople and the union never occurred. In the course of these proceedings, the Neoplatonist Bessarion supported the Roman church and gained the favor of Pope Eugenius IV, who made him a cardinal of the church (1439). Bessarion was drawn to the scholarly activity in Italy and remained there, encouraging young scholars by offering them use of his large library of books and manuscripts and translating Aristotle’s Metaphysics and Xenophon’s Memorabilia to spread the new learning to wider non-Greek-reading audiences. He rescued the mythological treatise of Pseudo-Apollodorus. Greek emigré scholars were welcome at his palazzo and he supported them by commissioning translations and transcriptions of ancient texts. Among the scholars he supported were Johannes Müller von Königsberg (Regiomontanus) and Nicolas of Cusa. Among the Greek exiles he supported were John Argyropoulos, Theodore Gaza, and George of Trebizond, a radical Aristotelian, against whose views Bessarion wrote arguably his most important work, In Calumniatorem Platonis. Bessarion was not so hard-line a Platonist as Pleitho, but he could not bear the misrepresentation of his beloved Plato by George. His approach was an attempt to reconcile the two philosophies by opening up religion to philosophy. In the meantime, he continued to serve diplomatic posts. He was legate at Bologna (1450-5) and often joined embassies to foreign princes, the last being a mission to Louis XI of France in 1471. In 1463 Pius II gave him the purely honorific title of patriarch of Constantinople, which made him primus Cardinalium (now called Dean of the Sacred College of Cardinals) and allowed him to preside over Papal conclaves in 1664 and 1471. He was considered at least twice for the papacy, starting in 1455, but was opposed by both sides of the unity question. Following his death his library, which had more than 900 Greek manuscripts was given to the senate of Venice and formed the nucleus of the Library of St. Mark.
L.Mohler, Kardinal Bessarion als Theologe, Humanist und Staatsmann (Paderborn 1923-42); L. Labowsky, Diz. Biog. Ital. s.v.