Octavian received the title of Augustus in 27 BC (Which means holy one) he restored elements of the Republic, with himself as princeps, or chief citizen.
Retaining the republican constitution, though as princeps Augustus held the real authority.
He could overrule the Senate and he controlled most of the Roman military.
The Senate retained some control of Rome, Italy, and the older, more peaceful provinces.
The frontier provinces, where legions were quartered, were governed by people appointed and controlled by Augustus.