The historical figure credited for the formulation of ethical principles of diplomacy is Niccolò Machiavelli. In his renowned work "The Prince," Machiavelli discusses the nature of power, leadership, and the often complex moral considerations involved in political governance. His pragmatic approach, emphasizing effectiveness over traditional morality, laid groundwork for modern political theory and international relations. Machiavelli's ideas address the often ambiguous intersection of ethics and statecraft, influencing political thought for centuries and sparking debate on the responsibilities of leaders in diplomacy.