Born Gaius Octavius, he was the great-nephew and adopted heir of Julius Caesar. After Caesar's assassination in 44 BC, Octavian formed the Second Triumvirate with Mark Antony and Lepidus to defeat Caesar's assassins.
The Triumvirate eventually broke apart, leading to a civil war between Octavian and Antony. Octavian's forces defeated Antony and Cleopatra at the Battle of Actium in 31 BC, leaving him the sole ruler of the Roman world.
In 27 BC, the Senate awarded him the title 'Augustus' (The Venerable). He initiated an era of relative peace and stability known as the Pax Romana, reformed the military and administration, and transformed Rome's infrastructure.