Emperors · Roman Empire Daily
Rome had no 'first emperor' until 27 BC, when the Senate gave Octavian the title Augustus.
Deep dive
After winning the civil wars, Octavian kept the forms of the Republic while holding real power. The Senate's grant of the name 'Augustus' is the conventional start of the Roman Empire.
Source: Res Gestae Divi Augusti; Suetonius, Augustus 7.