A coin of the late 3rd century emperor Probus
, showing abbreviated titles and honorifics - IMP·C·PROBUS·INVIC·P·F·AUG
Some thirty years before its first association with Caesar's heir, Augustus was an obscure honorific with religious associations. One early context (58 BC), associates it with provincial Lares (Roman household gods). In Latin poetry and prose it signifies the "elevation" or "augmentation" of what is already sacred or religious. Some Roman sources connected it to augury, and Rome was said to have been founded with the "august augury" of Romulus.
As Imperial name or title
The first true Roman Emperor known as "augustus" (and first counted as a Roman Emperor) was Gaius Julius Caesar Octavianus (Octavian). He was the adopted son and heir of Julius Caesar, who had been murdered for his seeming aspiration to divine monarchy, then subsequently and officially deified. Octavian studiously avoided any association with Caesar's claims, other than acknowledging his position and duties as Divi filius, "son of the deified one". Nevertheless, his position was unique, and extraordinary. He had ended Rome's prolonged and bloody civil war with his victory at Actium, and established a lasting peace. He was self-evidently favoured by the gods. As princeps senatus ("first man or head of the senate") he presided at senatorial meetings. He was pontifex maximus, chief priest of Roman state religion. He held consular imperium, with authority equal to the official chief executive, he was supreme commander of all Roman legions, and held tribunicia potestas ("tribunician power"). As a tribune, his person was inviolable (sacrosanctitas) and he had the right to veto any act or proposal by any magistrate within Rome. He was officially renamed Augustus by the Roman Senate on January 16, 27 BC – or perhaps the Senate ratified his own careful choice; "Romulus" had been considered, and rejected. So his official renaming in a form vaguely associated with a traditionally Republican religiosity, but unprecedented as a cognomen, may have served to show that he owed his position to the approval of Rome and its gods, and possibly his own unique, elevated, "godlike" nature and talents. His full and official title was Imperator Caesar Divi Filius Augustus.
Augustus' religious reforms extended or affirmed augusti as a near ubiquitous title or honour for various minor local deities, including the Lares Augusti of local communities, and obscure provincial deities such as the North African Marazgu Augustus. This extension of an Imperial honorific to major and minor deities of Rome and her provinces is considered a ground-level feature of Imperial cult, which continued until the official replacement of Rome's traditional religions by Christianity.
The title or name of Augustus was adopted by his successors, who held the name during their own lifetimes by virtue of their status, offices and powers. This included the Christian emperors. Most emperors also used imperator but others could and did bear the same title and functions. "Caesar" was used as a title, but was also the name of a clan within the Julian line.