Caesar Augustus (63 BC - 14 AD) was the first emperor of Rome, coming to power after a long period of civil wars and establishing both the Roman Empire and the Pax Romana, one the longest period of civil rest and expansion in the ancient world. Born Gaius Octavius, he was posthumously adopted by Julius Caesar following the latter's assassination in 44 BC. Historians generally refer to him as "Octavian" from that point until 27 BC, when he consolidated power and became Augustus.
Julius Caesar was his great-uncle, and took special interest in the boy, naming him his adopted son and heir in his will. For a brief time, Octavian ruled in the Second Triumvirate, along with Mark Antony and Marcus Aemilius Lepidus. However, following a series of wars and strife, Octavian defeated Antony and Cleopatra at the Battle of Actium in 31 BC. By 27 BC, he had gained political control over all of Rome, taking the position as First Princeps and the title of Augustus.
As emperor, Caesar Augustus expanded Roman territory through all of the Iberian Peninsula, parts of central Europe, North Africa, and Judea. He also undertook massive construction programs in Rome itself, as well as trying to produce legislation aimed at social reform.
Since he had no son, much of his later career was spent attempting to secure an heir, but all died and he eventually named his stepson Tiberius to succeed him as Emperor. Ancient historians long rumored that his Livia poisoned him, but proof of such an act is impossible to know.