Final answer:
The title "First Citizen" was used by rulers such as Augustus to emphasize a republican form of governance instead of a traditional monarchy, while still holding supreme power. This was also reflected in the United States' decision to use "Mr. President" as a title to prevent monarchal connotations and emphasize democratic values.
Step-by-step explanation:
Individuals adopted the title "First Citizen" instead of "king" or "emperor" as a means of distinguishing their rule from traditional monarchies and associations with hereditary rule or divinity, while still holding supreme power. For example, Augustus, the first Roman Emperor, chose the title "Princeps Civitatis", which translates to "First Citizen", to maintain the facade of the Republic despite having absolute authority. Similarly, after the American Revolution, the newly formed United States was keen to avoid any semblance of monarchy, which is reflected in the Framers' decision to prohibit titles of nobility in the Constitution and their eventually settling on the modest title of "Mr. President".
The adoption of titles by rulers can send a strong message about the nature of their governance. The title "First Citizen" implies a leader that is one among equals, promoting the ideals of republicanism and democracy, even if their powers are similar to that of a monarch. In history, this has often been a strategy of leaders who wished to present their power as being derived from the people or as custodians of the state rather than through divine right or hereditary succession.