Originally called Octavian; became Augustus later.
the first emperor (i.e. military commander), generally regarded as the founder of the "principate", as historians have agreed to call a monarchy that was still, in name, a republic and even a vague democracy for another two or three centuries. Augustus's father died when he was quite young, and he was eventually adopted by the Julius Caesar as his son and heir.
In 38 Octavian replaced his praenomen Gaius with Imperator, the title by which troops hailed their leader after military success (ultimately Imperator developed into the title Emperor). From this time Octavian's full title was Imperator Caesar Divi Filius, including the reference to him as the son of his deified father.