Around 431 BCE, Herodotus of Halicarnassus wrote up his Inquiry—in Greek, Historia—in which he sought to explain the origins and course of the conflicts between the Persians and the Greeks. This work inaugurated the western historical tradition and earned for its author the title Father of History. We’ll examine who Herodotus was, how he came to write his History, and why it is the indispensable source for the Persian Wars and the Battle of Thermopylae.