Augustus (Latin: IMPERATOR·CAESAR·DIVI·FILIVS·AVGVSTVS;Fully Imperator Caesar, Divi Filius, Augustus which means Imperator Caesar, Son of the Divus (Divus Julius), Augustus. 23 September 63 BC – 19 August AD 14These are the contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian after 45 BC. Due to departures from Julius Caesar's intentions, Augustus restored the Julian calendar in 8 BC, and the correspondence between the proleptic Julian calendar and the actual calendar observed in Rome is uncertain before 8 BC.(Blackburn & Holford-Strevens 2003: 670–1)), born Gaius Octavius Thurinus, was adopted by his great-uncle Julius Caesar in 44 BC, and between then and 27 BC was officially named Gaius Julius Caesar (Latin: CAIVS·IVLIVS·CAESAR). After 27 BC, he was named Gaius Julius Caesar Augustus. Because of the various names he bore, it is common to call him Octavius when refering to events between 63 and 44 BC, Octavian (or Octavianus) when refering to events between 44 and 27 BC, and Augustus when refering to events after 27 BC.

He became the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in AD 14. The young Octavius came into his inheritance after Caesar's assassination in 44 BC. In 43 BC, Octavian joined forces with Mark Antony and Marcus Aemilius Lepidus in a military dictatorship known as the Second Triumvirate. As a triumvir, Octavian ruled Rome and many of its provincesSome provinces were governed by the Senate. as an autocrat, seizing consular power after the deaths of the consuls Hirtius and Pansa and having himself perpetually re-elected. The triumvirate was eventually torn apart under the competing ambitions of its rulers: Lepidus was driven into exile, and Antony committed suicide following his defeat at the Battle of Actium by the fleet of Octavian in 31 BC.

After the demise of the Second Triumvirate, Octavian restored the outward facade of the Roman Republic, with governmental power vested in the Roman Senate, but in practice retained his autocratic power. It took several years to work out the exact framework by which a formally republican state could be led by a sole ruler; the result became known as the Roman Empire. The emperorship was never an office like the Roman dictatorship which Caesar and Sulla had held before him; indeed, he declined it when the Roman populace "entreated him to take on the dictatorship".CCAA, Erich S. Gruen, Augustus and the Making of the Principate, 35. By law, Augustus held a collection of powers granted to him for life by the Senate, including those of tribune of the plebs and censor. He was consul until 23 BC. His substantive power stemmed from financial success and resources gained in conquest, the building of patronage relationships throughout the Empire, the loyalty of many military soldiers and veterans, the authority of the many honors granted by the Senate, and the respect of the people. Augustus' control over the majority of Rome's legions established an armed threat that could be used against the Senate, allowing him to coerce the Senate's decisions. With his ability to eliminate senatorial opposition by means of arms, the Senate became docile towards his paramount position. His rule through patronage, military power, and accumulation of the offices of the defunct Republic became the model for all later imperial government.