This article seeks evidence of Herodotus's conception of his historical enterprise in the recurring scenes in which he portrays barbarian kings as inquirers and investigators. Through these scenes-involving most notably Psammetichus, Etearchus, Croesus, Cyrus, Cambyses, Darius, and Xerxes-the historian not only explores the character of autocrats, but also holds up a mirror to his own activity as inquirer. Once we recognize the metahistorical dimension of Herodotus's representation of inquiring kings, we can better understand the scenes in which these figures appear and the historian who sees his own enterprise reflected or distorted in their efforts. I argue first that the tale of Darius's inquiry concerning the Paeonian wonder-woman (5.12-13) is a paradigmatic Herodotean treatment of kingly inquiry in the way the historian both identifies with, and distances himself from, his kingly investigator. I then assess kingly research under three headings that reflect some of the many ways that Herodotean kings use and abuse investigation: Measurement and Self-Aggrandizement; Exploration and Conquest; Trial, Torture, and Test. Under the final rubric, kingly experiments are the focus, some involving human subjects (esp. 2.2 and 3.38), others involving the divine (1.46-49 and 7.12-18). Herodotus's extensive analysis of inquiring kings indicates that any earlier investigator-measurer, explorer, or experimenter-is a potential rival for him. If Herodotus is conscious that he is following in the footsteps of inquiring kings, however, his critique of their techniques and motives suggests that his inquiry is intellectually and ethically superior to theirs. Ultimately, then, Herodotus's exploration of regal investigation helps both to define and to lend authority to the historiê that he undertakes in the Histories.