Since its fall, the issue of succession to the Byzantine Empire has been a major point of contention both geopolitically, with different states laying claim to its legacy and inheritance, and among the surviving members of the Byzantine nobility and their descendants. Historically, the most prominent claims have been those of the Ottoman Empire, which conquered Byzantium in 1453 and ruled from its former capital, Constantinople; the Russian Empire, as the most powerful state practising Eastern Orthodox Christianity; and various nobles and figures in Western Europe of increasingly spurious and questionable imperial descent.

Constantinople fell to the Ottoman Empire on 29 May 1453, with the last emperor, Constantine XI Palaiologos, dying in the fighting. The Byzantine Empire was the medieval continuation of the ancient Roman Empire, its capital having been transferred from Rome to Constantinople in the 4th century by Rome's first Christian emperor, Constantine the Great. Though hereditary succession was often the norm, the Byzantine Empire was rooted in the bureaucracy of Ancient Rome, rather than the typical Western European ideas of hereditary inheritance. The accession of a new ruler was often a complex process and the empire lacked formal succession laws. Succession through illegitimate descent, adoption, or usurpation was not considered illegal and the rightful ruler was usually considered to be whoever was in possession of Constantinople at any given time. Most of the empire's prominent dynasties were founded through usurpation of the throne. As such, the Ottoman sultan Mehmed II, who had conquered Constantinople, proclaimed himself as the new emperor, as Kayser-i Rûm, in the aftermath of the conquest.

The Ottoman claim was not accepted internationally. Through marriage with the Palaiologos dynasty and through ruling the most powerful state adhering to the Eastern Orthodox Church, Russia historically also laid claim to succeed the Byzantine Empire, a claim the Russians attempted to enforce several times in the numerous Russo-Turkish wars. In the aftermath of 1453, those among the Byzantine nobility who had escaped the Ottoman conquest mainly looked to the surviving members of the Palaiologos dynasty as prospective emperors, with it being suggested by some to crown Demetrios Palaiologos (1407–1470), Constantine XI's brother, who ruled in the Morea. Demetrios was reluctant and was captured by the Ottomans in 1460. In 1483, Constantine XI's nephew, Andreas Palaiologos (1453–1502), in exile in Italy, proclaimed himself as the rightful emperor.

The last documented and verified legitimate male-line descendants of the Palaiologoi died out in the early 16th century with the death of the last Marquess of Montferrat of this line in 1533, but that did little to stop forgers, pretenders, impostors and eccentrics from claiming descent from the ancient emperors, not only the Palaiologoi but also earlier ruling dynasties of the empire, several of which did have descendants living beyond 1453. In cases, claimants and forgers claimed the imperial title itself. Some families gained relatively widespread recognition, such as the Angelo Flavio Comneno, supposed descendants of the Angelos dynasty. Some Byzantine claimants are still active today, despite the lack of formal Byzantine succession laws making finding a legitimate heir impossible. Such figures have often been accompanied by invented chivalric orders, typically with fabricated connections to the Byzantine Empire, despite the fact that chivalric orders were completely unknown in the Byzantine world. The last pretender to achieve significant recognition was the 19th-century forger Demetrius Rhodocanakis (1840–1902), though several less successful forgers and impostors have also appeared since his time. More sound claims to the Palaiologoi inheritance were grounded on legal, rather than genealogical, inheritance as well as on matrilineal descent. From the 16th century until their extinction in 1884, the Tocco family, the seniormost female-line descendants of Thomas Palaiologos, the father of Andreas Palaiologos, laid claim to represent the legitimate Byzantine imperial dynasty, though they did not claim any imperial titles. From 1494 to 1566, the kings of France publicly claimed to be the titular emperors of Constantinople on the grounds that Charles VIII of France had been sold the title by Andreas Palaiologos in 1494, though Andreas had later considered this sale invalid.

Byzantine succession practices

The Byzantine Empire was the medieval continuation of the ancient Roman Empire, with its capital having been transferred from Rome to Constantinople in the 4th century by Rome's first Christian emperor, Constantine the Great. The term "Byzantine" is an historiographical exonym: the people in the empire continually self-identified as "Romans" and referred to their empire as the "Roman Empire" throughout its existence.

As the successor of the ancient Roman emperors, the power of the Byzantine emperor (officially titled the "Emperor of the Romans"; in later times the "Emperor and Autocrat of the Romans") was nearly absolute; being the supreme judge, the sole legitimate legislator, the highest military commander and the protector of the Christian church. In Ancient Rome, before Christianization, the emperors were proclaimed as divine figures in their own right through the imperial cult, meaning that religious and political obedience were turned into the same thing. After Christianization, the absolute nature of imperial rule remained justified through the idea that the emperor, though no longer divine himself, was the divinely sanctioned ruler on Earth, on behalf of Jesus Christ. The emperor's role as the ruler of the Roman Empire and the leader of Christianity remained unquestioned within the empire itself until its fall. As such, Byzantine imperial ideology was simply an evolution of that of Ancient Rome. The Byzantines held the emperor to be dependent on no one when exercising his theoretically unlimited power, not accountable to anyone but God himself. The emperor's role as a divine viceroy of Earth meant that emphasis was placed on the emperor being physically perfect: deformities and certain conditions could make a candidate unsuitable for rule. Notably, blindness was typically seen as rendering an heir unsuitable, which is why many contenders for the throne were blinded throughout Byzantine history.

As the imperial office of Byzantium was an evolution of that of Ancient Rome, it was rooted in the bureaucracy of the Roman Republic rather than typical Western European ideas of hereditary monarchies. As a result, there were no formal succession laws in the empire and the rise of a new ruler was often a complex process. There was a senate in Constantinople, ostensibly the continuation of the ancient Roman Senate, but it had little real influence, only potentially playing an important role in the aftermath of the deaths of emperors, when it theoretically held the power to appoint the next ruler. The senate's role in the process wasn't as decisive as it had been in some portions of ancient Roman history; the dead emperor had often designated a successor in his lifetime, often even crowning his designated heir as co-emperor, and thus ratification by the senate was only a formality. If there was no clear designated successor, the succession often came down to either senatorial or (more frequently) military support. Having been acclaimed co-emperor was also not a sure way of eventually becoming the sole ruling emperor. It was common for co-emperors to be blinded or killed once the power of their senior co-ruler had been compromised. Imperial children proclaimed as co-emperors that were still infants at the time of their father's death were often deposed or killed. The complex succession practices, and the threat of a general being proclaimed as emperor by the army, often resulted in civil war.

In the ancient Roman Empire, the imperial throne tended to be passed on through dynastic succession, but only if a reasonable dynastic candidate existed and could garner enough support and loyalty from the bureaucrats and generals of the empire. As an example, Emperor Jovian (363–364) left two sons who were passed over after his death. Upon the death of Eastern emperor Valens in 378, his nephews Valentinian II and Gratian, who ruled in the west, were deemed too young to rule the east as well and the unrelated Theodosius I was proclaimed Eastern emperor. Likewise, succession in the later Byzantine Empire was also often de facto hereditary, with emperors crowning their sons as co-emperors for generations to ensure their inheritance, leading to the creation of dynasties. At times when the empire was stable and at peace, succession through primogeniture (eldest son inherits) was the custom, if the emperor had a son it was expected that this son would inherit imperial power, but while this practice had been largely de facto adopted by the Middle Ages, there were several exceptions and it had not been formally codified as law. Though the vast majority of emperors were male, men and women were theoretically equally eligible for the throne (there were three ruling empresses; Irene, Zoë, and Theodora, and numerous powerful female regents, such as Eudokia), and a ruling emperor did not necessarily have to raise their oldest son to be co-emperor, but could designate whichever son deemed the most fit to be successor. Some preference was often granted to children born after their parents had become emperors, who were designated as porphyrogenitus ("born in the purple"). In some cases, illegitimate children rose to the throne and in other cases, emperors adopted heirs with whom they had no relation at all.

The lack of formal hereditary succession in the Byzantine Empire was clearly illustrated during the events of the Fourth Crusade in 1202–1204, when Crusaders arrived at Constantinople with the aim of placing Alexios IV Angelos on the throne of the Byzantine Empire. Alexios IV's father Isaac II had been deposed by his brother (and Alexios IV's uncle), Alexios III, in 1195. Although Alexios IV would have been the rightful heir of Isaac II from the perspective of the Crusaders from Western Europe, the citizens of the empire itself were unconcerned with his cause as Alexios III, according to their own customs, was not an illegitimate ruler in the way he would have been in the West. Of the 94 emperors who reigned from Constantinople's proclamation as Roman capital in 330 to the city's fall in 1453, 20 had started their careers as usurpers. Because obtaining the throne through usurpation wasn't seen as illegitimate, revolts and civil wars were frequent in the empire; more than thirty of its emperors had to face large-scale revolts against their rule. Many of the empire's most prominent dynasties, including the Macedonian, Komnenos, Angelos and Palaiologos dynasties, were all founded through usurpers seizing power by displacing a previous ruling dynasty. Because of the complex succession practices of the Byzantine Empire, each emperor could in some way be seen as having founded a new imperial dynastic line. This makes any attempt at determining a "rightful heir" to the Byzantine Empire impossible, especially given that descent through adoption or illegitimate birth would not have barred a Byzantine noble from assuming the throne.

Claims of imperial succession

Ottoman Empire