Wikipedia has more information on the Byzantine Emperor, who lived from 1350 to 1425, and has recently been cited by Pope Benedict:
Created despotēs by his father, the future Manuel II traveled west to seek support for the Byzantine Empire in 1365 and in 1370, serving as governor in Thessalonica from 1369. The failed attempt at usurpation by his older brother Andronikos IV Palaiologos in 1373 led to Manuel being proclaimed heir and co-emperor of his father. In 1376–1379 and again in 1390 they were supplanted by Andronikos IV and then his son John VII, but Manuel personally defeated his nephew with help from the Republic of Venice in 1390. Although John V had been restored, Manuel was forced to go as an honorary hostage to the court of the Ottoman Sultan Bayezid I at Prousa (Bursa). During his stay, Manuel was forced to participate in the Ottoman campaign that reduced Philadelpheia, the last Byzantine enclave in Anatolia.
Hearing of his father's death in February 1391, Manuel II Palaiologos fled the Ottoman court and secured the capital against any potential claim by his nephew John VII. Although relations with John VII improved, the Ottoman Sultan Bayezid I besieged Constantinople from 1394 to 1402. After some five years of siege, Manuel II entrusted the city to his nephew and embarked on a long trip to western courts (including those of the Kingdom of England, France, the Holy Roman Empire, and Aragon) to seek assistance against the Ottoman Empire.
Meanwhile an anti-Ottoman crusade led by the Hungarian King Sigismund of Luxemburg failed at the Battle of Nicopolis on September 25, 1396, but the Ottomans were themselves crushingly defeated by Timur at the Battle of Ankara in 1402. As the sons of Bayezid I struggled with each other over the succession in the Ottoman Interregnum, John VII was able to secure the return of the European coast of the Sea of Marmara and of Thessalonica to the Byzantine Empire. When Manuel II returned home in 1403, his nephew duly surrendered control of Constantinople and was rewarded with the governorship of newly recovered Thessalonica.
Manuel II Palaiologos used this period of respite to bolster the defenses of the Despotate of Morea, where the Byzantine Empire was actually expanding at the expense of the remnants of the Latin Empire. Here Manuel supervised the building of the Hexamilion (six-mile) wall across the Isthmus of Corinth, intended to defend the Peloponnese from the Ottomans.
Manuel II stood on friendly terms with the victor in the Ottoman civil war, Mehmed I (1402–1421), but his attempts to meddle in the next contested succession led to a new assault on Constantinople by Murad II (1421–1451) in 1422. During the last years of his life, Manuel II relinquished most official duties to his son and heir John VIII Palaiologos, and in 1424 they were forced to sign a peace treaty with the Ottoman Turks, whereby the Byzantine Empire undertook to pay tribute to the sultan. Manuel II died on 21 July 1425.
