|Octavian (Later know as Augustus).|
In 44 BC Octavian had been adopted posthumously by his maternal great-uncle Gaius Julius Caesar following Caesar's assassination. Together with Mark Antony and Marcus Lepidus, he formed the Second Triumvirate to defeat the assassins of Caesar. Following their victory at Phillipi, the Triumvirate divided the Roman Republic among themselves and ruled as military dictators. The Triumvirate was eventually torn apart under the competing ambitions of its members: Lepidus was driven into exile and stripped of his position, and Antony committed suicide following his defeat at the Battle of Actium by Augustus in 31 BC.
It is under Octavian, rather than his great uncle Caesar, that the actual Roman Empire began. The Roman Republic had been an oligarchic republic with state power shared by several key Roman families. After the demise of the Second Triumvirate, Octavian restored the outward facade of the free Republic, with governmental power vested in the Roman Senate, the executive magistrates, and the legislative assemblies. In reality, however, he retained his autocratic power over the Republic as a military dictator. By law, Augustus held a collection of powers granted to him for life by the Senate, including supreme military command, and those of tribune and censor. It took several years for Augustus to develop the framework within which a formally republican state could be led under his sole rule. He rejected monarchical titles, and instead called himself Princeps Civitatis ("First Citizen").
The Roman Republic was never restored, but neither was it ever formally abolished (the term res publica continued to be used to refer to the state apparatus), so the exact date of the transition to the Roman Empire is a matter of interpretation. Historians have proposed the Roman Senate's grant of extraordinary powers to Octavian under the first settlement and his adopting the title Augustus in 27 BC, as the defining event ending the Republic.The month of August is named after Augustus; until his time it was called Sextilis (named so because it had been the sixth month of the original Roman calendar and the Latin word for six is sex). Commonly repeated lore has it that August has 31 days because Augustus wanted his month to match the length of Julius Caesar's July, but this is an invention of the 13th century scholar Johannes de Sacrobosco. Sextilis in fact had 31 days before it was renamed, and it was not chosen for its length. According to a senatus consultum quoted by Macrobius, Sextilis was renamed to honor Augustus because several of the most significant events in his rise to power, culminating in the fall of Alexandria, fell in that month.