Thucydides (c. 460 – c. 400 BC), an Athenian historian and general, is renowned for his work, History of the Peloponnesian War, which chronicles the fifth-century BC conflict between Sparta and Athens up to the year 411 BC. Acclaimed as the father of "scientific history," Thucydides is praised for his stringent standards of impartiality, evidence-gathering, and cause-and-effect analysis, all conducted without attributing events to divine intervention, as he elucidated in the introduction to his work.

Moreover, Thucydides is heralded as the progenitor of political realism, a perspective that interprets the political actions of individuals and the outcomes of state relations through the lenses of fear and self-interest. His contributions extend beyond historical narrative; his text is a staple in global universities and military colleges. The Melian dialogue, in particular, is esteemed as a foundational text in international relations theory, while his rendition of Pericles' Funeral Oration continues to be a subject of study among political theorists, historians, and classicists. Thucydides' insights into human nature, as applied to crises like plagues, massacres, and wars, have engendered a deeper understanding of behavioral motivations.