Octavius, later known as Augustus, was Rome's first emperor who rose to power after the assassination of Julius Caesar. He formed the Second Triumvirate with Mark Antony and Lepidus to defeat Caesar's assassins. After defeating Antony in battle, Octavius consolidated control over Rome and established the Principate, where he ruled as the first emperor but allowed the senate to retain some powers. His reign from 27 BC to 14 AD marked the beginning of the Pax Romana period of peace and territorial expansion for Rome.