This article explores the official duties of the hazarapat (hazarapatiš) at the court of the Achaemenid kings and defines the relationship between the terms chiliarch (χιλíαρχος) and isangeleus (εἰσαγγελεύς), both used for this Persian title, in the evolution of the ancient written tradition. Ancient Greek authors, up to Ctesias of Cnidus, discussed the chiliarch only in the military context. In later periods, it was increasingly perceived as both the Persian king’s bodyguard and the isangeleus at court ceremonies, thus implying broad political powers. In reality, the chiliarch never combined these two duties. He remained the commander of his military unit, which consisted of a thousand of men, and apparently checked the reliability of royal visitors before audiences. The isangeleus, another royal courtier, was responsible for informing the king about the intentions of visitors, as well as for guiding their adherence to Persian etiquette and customs.