Why did Augustus call himself princeps instead of king?

Augustus avoided the title of king because he sought to maintain the appearance of restoring the Roman Republic, which had been severely damaged by the civil wars of the 1st century BCE. By adopting the title princeps—which historically referred to the princeps senatus, or the leading member of the Senate—he lent plausibility to his claim that he was a restorer of traditional republican institutions rather than an autocrat.1

His decision was rooted in a desire for political respectability and a deep respect for ancestral custom, especially following the fate of Julius Caesar, who had been assassinated for his perceived monarchical ambitions. Augustus preferred to be viewed as the "first citizen" of Rome, a label that allowed him to exercise supreme power while avoiding the resentment associated with the title of king or military despot. Through this pragmatic approach, he successfully established the principate, a system of government that maintained the facade of republican governance while centralizing authority under his own leadership.213