The Greek god Zeus is sometimes called Zeus Xenios in his role as a protector of guests. He thus embodied the religious obligation to be hospitable to travelers. Theoxeny or theoxenia is a theme in Greek mythology in which human beings demonstrate their virtue or piety by extending hospitality to a humble stranger (xenos), who turns out to be a disguised deity (theos) with the capacity to bestow rewards. These stories caution mortals that any guest should be treated as if potentially a disguised divinity and help establish the idea of xenia as a fundamental Greek custom.
Source: Xenia (Greek) – Wikipedia