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.
Final War of the Roman Republic
Following the end of the war, Octavian brought peace to the Roman state that had been plagued by a century of civil wars. Octavian became the most powerful man in the Roman world and the Senate bestowed upon him the name of Augustus in 27 BC. Octavian, now Augustus, would be the first Roman Emperor and would transform the oligarchic/democratic Republic into the autocratic Roman Empire.