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.
Constitution of the Roman Empire
The general who won the last civil war of the Roman Republic, Gaius Octavian, became the master of the state. In the years after 30 BC, Octavian set out to reform the Roman constitution. The ultimate consequence of these reforms was the abolition of the republic and the founding of the Roman Empire. When Octavian deposed his fellow triumvir, Mark Antony, in 32 BC, he resigned his position as triumvir, but was probably vested with powers similar to those that he had given up. Octavian wanted to solidify his status as master of the state whilst avoiding assassination.