The title Augustus is understood to roughly translate as “the illustrious one” and, although the title did not grant him political authority, many historians see this as the point at which Augustus’ rule as first Roman Emperor began.
Octavian’s rise to power, and his position as Emperor, was achieved over a long period of time. Julius Caesar was his great-uncle, and in Caesar’s will was declared his adopted son and heir. Consequently he inherited Caesar’s property and lineage, but also a number of titles and offices that had been bestowed upon his adoptive father. Octavian had already proved himself a formidable general, but his position as Caesar’s heir won him further support from many veteran legionnaires.
Octavian’s assumption of the role of an Emperor was achieved by effectively collecting a further range of powers as Princeps Civitatis, which translates as "First Citizen of the State". These were voluntarily granted to him for life by the Senate.
In fact when he appeared before them in 27 BCE to return the powers he had already accumulated, the Senate requested he remain and even extended his authority. Consequently his position was in keeping with the traditions of the Republic as his powers came from the Senate, but in practice he wielded exclusive political power.
Furthermore, having been granted control of the more problematic provinces of the empire, the Senate had effectively given him control of the vast majority of the Roman army, which further guaranteed his dominance of Roman politics.