Roman Emperor

Augustus Caesar (r. 27 B.C.-14 A.D.)
Following the assassination of Julius Caesar on March 14, 44 B.C. Octavian the grand nephew and adopted son of Julius Caesar, Marc Antony, a Roman consul and Marcus Aemilius Lepidus, a high-ranking Roman official who had served under Julius Caesar, formally constituted a three-man ruling body, referred to as a triumvirate, to take Caesar’s place. They fought Caesar’s assassins, defeating Brutus and Cassius at the Battle of Philippi in 42 B.C. and executed Cicero. Octavian learned of his adoption while he was out of the country and after Julius Caesar's death. He eventually won acceptance into Caesar's family and inherited his estates, then changing his family name of Julius Caesar's and became known as Augustus.

In or sometime before 14 B.C., at the age of 76, Augustus had an account of his deeds, accolades and his expenditures recounted and later posted on markers in various parts of the Empire upon his death. With regard to the events following the assassination of Julius Caesar, the account simply says he freed the state from a faction, was named propraetor, consul and a triumvir in his 19th year (or 20th) and punished the assassins who slaughtered his father and defeated them in two battles.

The triumvirate ruled more or less without crises for five years. However, the seeds of discord, arguably sown during the few months following Caesar’s death, between Antonius and Octavian, lent impetus to the eventual disintegration of the three-man government which was renewed once and then came to an end with the defeat and death of Antonius and the exile of Lepidus.

Octavian, Augustus Caesar, took the throne in 27 B.C. During his forty-year rule he began building the political structure for Imperial Rome. The system of magistracies was subsumed by the throne and were awarded by the emperor (princeps in Latin).

Caesar Augustus also took over direct control of the majority of the provinces, ruling through his appointed subordinates, and nationalised the army, placing it under direct control of the emperor. This measure stripped generals of the power to interfere in politics with their troops in support as had been done earlier by Julius Caesar in 49 B.C..

Augustus invested heavily in changing Rome’s physical stature with extensive building projects to ostentatiously advertise his rule. Concomitantly, he went to great lengths to promote his own family as the future imperial dynasty.

When Augustus died in 14 A.D., he was succeeded by his step-son Tiberius.

Nero (r. 54-68)
Nero Claudius Caesar Augustus Germanicus, commonly referred to as Nero, was Roman Emperor from A.D. 54 to his death in A.D. 68. He succeeded the Emperor Claudius, who had adopted him in A.D. 50; Claudius already had a son, Britannicus.

Year of the Five Emperors (193)
Following the assassination of Commodus, there were four others who ruled as emperors within approximately one year of his death.

Publius Helvius Pertinax (r. December 31, 192 - March 28, 193)
Pertinax served as the commander in chief of the army along the Danube, and later, governor of Mœsia, Dacia, and Syria under Marcus Aurelius. Under Commodus, he was commander-in-chief in Britain and  was then appointed governor in Africa, eventually becoming prefect of the city of Rome. Pertinax was banished later when a plot to assassinate Commodus was uncovered.

Following the assassination of Commodus on 31 December, 192, at the age of 66 Pertinax was declared Emperor by the army at the request of the prefect of the Prætorian Guard, Lætus. Later this was confirmed by the Senate at Pertinax's request. The Prætorian Guard however led a coup which Pertinax personally confronted and was killed trying to quell. The entire duration of his rule was only 87 days.

Publius Septimius Geta (r. 209 - Dec. 26, 211)
Co-ruler with his father Septimius and his older brother Marcus Aurelius Antoninus.

The Crises of the Third Century
During the period 235 to 284, the Roman Empire was beset by invasions, usurpations, and civil war. Of the thirty-five who served as emperor, only one died a natural death. After the assassination of the Emperor Severus Alexander in 235, the army declared successors that were either not accepted by the senate or done so under duress. Germans and Goths threatened the northern frontier of the Empire, the Sassanid Dynasty of Persia from 226 onward threatened the Empire from the East and actually captured and possibly executed one emperor, Valerian. Separatists states emerged in Gaul and Palmyra. The economy was in peril: coinage was debased, there was a decline in population and agricultural productivity suffered.

The ascension of Valerian seemed at one point to mark an end to the turmoil but Valerian was captured in his campaign against the Sassanid Dynasty and never returned to Rome.

While some of the emperors did in fact stem the tide of invasions and rebellions, the Empire did not see an extended period of stability until the ascension of Diocletian.

This period signifies the demarcation between the Principate and Dominate: the early and the late Roman Empire. During the Principate period the emperors primarily acted as guides, commanders-in-chief, and leaders. During the Dominate period the emperors tended to be autocrats ruling with absolute power.

With Diocletian's death in 308, there was another period of instability until Constantine was able to gain control in 324.

Gaius Iulius Verus Maximinus (r. 235–238)
Also known as Maximinus Thrax (i.e. Maximinus the Thracian) and Maximinus I

Marcus Antonius Gordianus Pius (r. 238 - 244)
Also known in English as Gordian III

Marcus Julius Philippus (r. 244 to 249)
Also known as Philippus I Arabs and in English as Philip the Arab.

Gaius Messius Quintus Traianus Decius (r. 249 - 251)
Decius was killed in his campaign against the Goths.

Herennius Etruscus (r. 251)
Co-ruler with his father Gaius Messius Quintus Traianus Decius

Titus Julius Priscus (251)
Proclaimed Emperor but never accepted by the senate.

Gaius Valens Hostilianus Messius Quintus (r. 251)
Co-ruler with his brother Gaius Vibius Trebonianus Gallus

Gaius Vibius Volusianus (r. 251 - 253)
Co-ruler with his father Gaius Vibius Trebonianus Gallus and his uncle Gaius Valens Hostilianus Messius Quintus.

Publius Licinius Valerianus (r. 253 - 260)
Known in English as Valerian. Captured in the campaign against the Sassinid Dynasty and died in captivity.

Publius Licinius Egnatius Gallienus (r. 253 - 268)
Ruled as co-emperor with his father Valerian from 253 to 260, and then as the sole Roman emperor from 260 to 268. Gallienus appointed Odenathusm, his general in Palmyra, the position of King. Odenathusm was successful in fighting the Sassanid Persians and various usurpers but never attempted to usurp the imperial throne. Upon his death, his wife Zenobia took the title Augustus and ruled in her son's name over Syria, Palestine, Roman Arabia, and parts of Egypt and Asia Minor. Zenobia was later defeated by the Emperor Aurelian.

Marcus Aurelius Claudius Augustus Gothicus (r. 268 - 270)
Often referred to as Claudius II.

Lucius Domitius Aurelianus (r. 270–275)
Known in English as Aurelian.

Marcus Annius Florianus (276)
Marcus was chosen by the army and while he may actually have ruled, he was never accepted by the senate.

Marcus Aurelius Carinus (r. 283 – July, 285)
Elder son of Marcus Aurelius Carus.

Gaius Aurelius Valerius Diocletianus (r. November 20, 284 to May 1, 305)
Known in English as Diocletian. His ruled effectively brought an end to a period of instability dating from about 235.