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.
Fall of the Western Roman Empire
By convention, the Western Roman Empire is deemed to have ended on 4 September 476, when Odoacer deposed Romulus Augustulus and proclaimed himself ruler of Italy, but this convention is subject to many qualifications. In Roman constitutional theory, the Empire was still simply united under one emperor, implying no abandonment of territorial claims. In areas where the convulsions of the dying Empire had made organized self-defence legitimate, rump states continued under some form of Roman rule after 476. Julius Nepos still claimed to be Emperor of the West and controlled Dalmatia until his murder in 480. Syagrius son of Aegidius ruled the Domain of Soissons until his murder in 487. The indigenous inhabitants of Mauretania developed kingdoms of their own, independent of the Vandals, with strong Roman traits. They again sought Imperial recognition with the reconquests of Justinian I, and they put up effective resistance to the Muslim conquest of the Maghreb. While the civitates of Britannia sank into a level of material development inferior even to their pre-Roman Iron Age ancestors, they maintained identifiably Roman traits for some time, and they continued to look to their own defence as Honorius had authorized.