Thucydides (c. 460-400 BCE) was an ancient Greek historian and Athenian general, best known for writing the "History of the Peloponnesian War," which chronicles the conflict between Athens and Sparta from 431-404 BCE.

He's considered one of the first true historians because of his rigorous approach to recording events. Unlike his predecessor Herodotus, who often included myths and legends, Thucydides focused on eyewitness accounts, participant testimony, and documentary evidence. He aimed to create an accurate, factual record rather than an entertaining narrative.

Thucydides personally participated in the war as an Athenian general but was exiled in 424 BCE after failing to prevent the capture of Amphipolis by the Spartans. This exile, while personally devastating, allowed him to travel freely and gather information from both sides of the conflict.

His work is notable for several reasons:

• He introduced the concept of political realism, analyzing power dynamics between states

• He excluded divine intervention as an explanation for events, focusing on human motivations

• He included detailed speeches (though likely reconstructed) that revealed the thinking of key figures

• He emphasized the importance of understanding cause and effect in historical events

His famous "Melian Dialogue" remains influential in international relations theory, illustrating the brutal reality that "the strong do what they can and the weak suffer what they must." His analysis of how democracy can lead to demagoguery and poor decision-making during wartime also continues to resonate with political theorists today.