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.
Ambrosius Aurelianus
In Valerio Massimo Manfredi's "The Last Legion", Aurelianus (here called "Aurelianus Ambrosius Ventidius") is a major character and is shown as one of the last loyal Romans, going to enormous lengths for his boy emperor Romulus Augustus, whose power has been wrested by the barbarian Odoacer. In this story, Romulus Augustus marries Igraine, and King Arthur is their son, and the sword of Julius Caesar becomes the legendary Excalibur in Britain. In the 2007 film version of the novel, he is played by Colin Firth and his name becomes "Aurelianus Caius Antonius". In both he is called "Aurelius" for short.