Caesar Augustus, also known as Octavian, was the first Roman emperor, reigning from 27 BC until his death in AD 14. His status as the founder of the Roman Principate has consolidated a legacy as one of the most effective leaders in human history. The reign of Augustus initiated an era of relative peace known as the Pax Romana. The Roman world was largely free from large-scale conflict for more than two centuries, despite continuous wars of imperial expansion on the Empire's frontiers and the year-long civil war known as the "Year of the Four Emperors" over the imperial succession.
Originally named Gaius Octavius, he was born into an old and wealthy equestrian branch of the plebeian gens Octavia. His maternal great-uncle Julius Caesar was assassinated in 44 BC and Octavius was named in Caesar's will as his adopted son and heir; as a result, he inherited Caesar's name, estate, and the loyalty of his legions. He, Mark Antony and Marcus Lepidus formed the Second Triumvirate to defeat the assassins of Caesar. Following their victory at the Battle of Philippi, the Triumvirate divided the Roman Republic among themselves and ruled as de facto dictators. The Triumvirate was eventually torn apart by the competing ambitions of its members; Lepidus was exiled in 36 BC and Antony was defeated by Octavian at the Battle of Actium in 31 BC.