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.
Roman Empire
The Roman Empire (, ; Koine and Medieval Greek: Βασιλεία τῶν Ῥωμαίων, tr. ) was the post-Roman Republic period of the ancient Roman civilization. It had a government headed by emperors and large territorial holdings around the Mediterranean Sea in Europe, North Africa, and West Asia. From the constitutional reforms of Augustus to the crisis of the third century, the Empire was a principate ruled from the city of Rome (27 BC - 285 AD). The Roman Empire was then divided between a Western Roman Empire, based in Milan and later Ravenna, and an Eastern Roman Empire, based in Nicomedia and later Constantinople, and it was ruled by multiple emperors (with the exception of the sole rule of Constantine between 324 and 337, and Theodosius between 392 and 395). The Western Empire collapsed when Ravenna fell to the Germanic Herulians of Odoacer in 476 AD. The end of the Western Roman Empire is traditionally used to mark the end of ancient Rome. The Eastern Empire, known in the post-Roman West as the Byzantine Empire, collapsed when Constantinople fell to the Ottoman Turks of Mehmed II in 1453.