The Roman Emperor was the ruler of the Roman Empire during the imperial period (starting in 27 BC). The emperors used a variety of different titles throughout history, usually Augustus or Caesar. Another title often used was imperator, originally a military honorific. Early Emperors also used the title princeps (first citizen). Emperors frequently amassed republican titles, notably Princeps senatus, Consul, and Pontifex Maximus.

The legitimacy of an emperor's rule depended on his control of the army and recognition by the Senate; an emperor would normally be proclaimed by his troops, or invested with imperial titles by the Senate, or both. The first emperors reigned alone; later emperors would sometimes rule with co-Emperors and divide administration of the Empire between them.

The Romans considered the office of emperor to be distinct from that of a king. The first emperor, Augustus, resolutely refused recognition as a monarch. Although Augustus could claim that his power was authentically republican, his successor, Tiberius, could not convincingly make the same claim. Nonetheless, for the first three hundred years of Roman Emperors, from Augustus until Diocletian, a great effort was made to emphasize that the Emperors were the leaders of the Roman Republic. During the 4th and 5th centuries, while emperors ruled in an openly monarchic style and did not preserve the nominal principle of a republic, the contrast with "kings" was maintained, and elements of the Republican institutional framework (senate, consuls, and magistrates) were preserved until the very end of the Western Empire.

In addition to their pontifical office, some emperors were given divine status after death. With the eventual hegemony of Christianity, the emperor came to be seen as God's chosen ruler, as well as a special protector and leader of the Christian Church on Earth, although in practice an emperor's authority on Church matters was subject to challenge.

The Western Roman Empire collapsed in the late 5th century. Romulus Augustulus is usually considered to be the last emperor of the west after his forced abdication in 476, although Julius Nepos maintained a claim to the title until his death in 480, and the Byzantine and Ottoman Emperors) styled themselves "Emperor of the Romans" until the latter empire fell in 1922.

The works of Harry Turtledove have made the following use of Roman Emperors.

Gunpowder Empire

In an alternate known as Agrippan Rome, the Roman General Marcus V. Agrippa lived three decades longer than in the home timeline, and won great victories that stabilized the Empire so that it endured to the present day.

Emperor Reign
1 Augustus Augustus.jpg 27 BC-AD 14
2 Agrippa Agrippa.jpg AD 14-26
3 Lucius Lucius.jpg AD 26-?
4-? All unnamed 1st through 21st centuries
? Honorio Prisco III Nophoto.jpg Incumbent at novel's end, 2095

Other Emperors

Augustus is Emperor and a POV in Give Me Back My Legions!, set in OTL.

Tiberius is referenced as the reigning Caesar (personal name not given) in "Shock and Awe", an alternate history.

Antoninus Pius is referenced as the reigning Emperor in "Death in Vesunna", a science fiction story set in OTL.

Marcus Aurelius appears as Emperor in Household Gods, a fantasy set in OTL.

Other Turtledove works make significant posthumous references to Emperors who died before the relevant Point of Divergence.

Historical Emperors in non-imperial roles

Tiberius is referenced as a General in Give Me Back My Legions!, set in OTL before he became Emperor.

See also