Constantine XI - Basileus of Basileía Rhōmaíōn from 1449 to 1453
Constantine XI was the last reigning Byzantine Emperor, ruling as a member of the Palaiologos dynasty from 1449 to his death in battle at the fall of Constantinople in 1453.

Previously serving as regent for his brother John VIII 1437–1439, Constantine succeeded his brother, who died in Constantinople of natural causes in 1448, as Emperor following a short dispute with his younger brother Demetrios. Despite the mounting difficulties of his reign, contemporary sources generally speak respectfully of Constantine. Constantine would rule for just over 4 years, his reign culminating in the Ottoman siege and conquest of Constantinople, the imperial capital, under Sultan Mehmed II.

Constantine did what he could to organize the defenses of the city, stockpiling food and repairing the old Theodosian walls, but the reduced domain of the Empire and the poor economy meant that organizing a force large enough for the defense of the city was impossible. Constantine led the defending forces, numbering approximately 7,000, against an Ottoman army numbering around 10 times that and died in the ensuing fighting.
Constantine XI
Emperor Constantine XI of the Byzantine Empire