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.
Western Roman Empire
Imperial rule continued in Sicily throughout the eighth century, with the island slowly being overrun by the Arabs during the course of the ninth century. In Italy, a few strongholds in Calabria provided a base for a later, modest imperial expansion, which reached its peak in the early eleventh century, with most of southern Italy under Roman rule of a sort. This, however, was undone by further civil wars in the Empire, and the slow conquest of the region by the Empire's former mercenaries, the Normans, who finally put an end to imperial rule in Western Europe in 1071 with the conquest of Bari. The last Emperor to attempt reconquests in the West was Manuel I Komnenos, who invaded southern Italy during a war with the Norman Kingdom of Sicily in the 1150s. The city of Bari willingly opened its gates to the Emperor and after successes in taking other cities in the region, Manuel dreamed of a restored Roman Empire and a union between the churches of Rome and Constantinople, separated since the schism of 1054. Despite initial successes and Papal support, the campaign was unsuccessful and Manuel was forced to return east.