The present thesis aims to analyse the manner in which the ethnically and culturally diverse environment of Eastern Anatolia during the Hellenistic era has influenced the royal houses of the Mithradatids, Ariarathids, Ariobarzanids and Commagenian Orontids. The focus of analysis will be represented by the contact and osmosis between two of the major cultural influences present in the area, namely the Iranian (more often than not Achaemenid Persian) and Greco-Macedonian, and the way in which they were engaged by the ruling houses, in their attempt to establish, preserve and legitimise their rule. This will be followed in a number of fields: dynastic policies and legitimacy conceptions, religion, army and administration. In each of these fields, discrete elements betraying the direct influence of one or the other cultural traditions will be followed and examined, both in isolation and in interaction with other elements, together with which they form a diverse, but nevertheless coherent whole. The eventual result of this analysis will be to demonstrate how the intersection of cultures and the willing appropriation by the ruling houses of what we might call, using a modern term, ‘multiculturalism’ has created a new, interesting and robust tradition, whose influence would endure well into the Roman era.