Roman emperor
The Western Roman Empire collapsed in the late 5th century. Romulus Augustulus is often considered to be the last emperor of the West after his forced abdication in 476, although Julius Nepos maintained a claim recognized by the Eastern Empire to the title until his death in 480. Following Nepos' death, the Eastern Emperor Zeno abolished the division of the position and proclaimed himself as the sole Emperor of a reunited Roman Empire. The Eastern imperial lineage continued to rule from Constantinople ("New Rome"); they continued to style themselves as Emperor of the Romans (later βασιλεύς Ῥωμαίων in Greek), but are often referred to in modern scholarship as Byzantine emperors. Constantine XI Palaiologos was the last Roman emperor in Constantinople, dying in the Fall of Constantinople to the Ottomans in 1453.
Last Roman Emperor
The legend is based on the "Apocalypse of Pseudo-Methodius", which was, after the Book of Daniel and the Book of Revelation, "the most widespread apocalypse story in Europe". It proposes a different Last Emperor from the previous figure, who fought against religious enemies, and introduced the conflict with Islam: he will "go forth against them [the enemies of the faith] from the Ethiopian sea and will send the sword and desolation into Ethribus their homeland, capturing their women and children living in the Land of Promise". After conquering his enemies he would travel to Jerusalem and relinquish his power on the Mount of Olives. The Last Emperor was further developed in the writings of Adso of Montier-en-Der, whose "Libellus de Antichristo" (ca. 954) was a popular biography of the Antichrist, whose coming was preceded by the rise of a Frankish ruler (the continuation of the Roman Empire); this Last Emperor would voluntarily give up his power and die, after which the Antichrist comes to power. Another important impetus came from the oracles of the Tiburtine Sibyl, first recorded in Latin around the year 1000; its legend proved particularly adaptable to rulers all over Europe, containing as it did a list of emperors and kings leading up to the Last Emperor which could be revised or added to as political and dynastic circumstances required. It still had great currency in the fifteenth century.