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.
Probus (emperor)
According to the favorable treatment of Gibbon (whose account is largely derived from the "Augustan History"), Probus was the last of the benevolent constitutional emperors of Rome. While his successor Carus (Imp. 281-284) simply disdained to seek the senate's confirmation of his title, the latter's successor Diocletian (Imp. 284-305) took active measures to undermine its authority, and established the autocratic nature and divine deriviation of the Imperial power. Never again, after Diocletian's reforms, would the Roman senate play an active role in the management of the empire. On the military sphere, Probus' victories continued the succession of martial Illyrian emperors begun by Claudius Gothicus, which restored the military supremacy of Rome after defeats sustained during the crisis of the third century.Attribution: