Sacred kingship is the arrangement in which a ruler holds a religious standing as well as a political one, as a god, a descendant of gods, a divinely appointed agent, or the necessary mediator between a community and the divine. It is among the most widely attested political-religious forms in history.
The degrees vary considerably, and the differences matter more than the similarity. The Egyptian pharaoh was identified with Horus in life and Osiris in death and was a god in a strong sense, though Egyptologists continue to debate how the claim was understood in practice and note that pharaohs are also depicted worshipping. Mesopotamian kings were generally chosen by the gods rather than being gods themselves, with a few deliberate exceptions who claimed divinity and were unusual for it. Roman emperors were deified after death and, in the eastern provinces, during life, and the imperial cult became the precise point at which Jewish and then Christian refusal turned into a capital matter. Japanese emperors were held to descend from Amaterasu, a claim formally set aside by Hirohito in 1946 under the occupation. Chinese emperors held the Mandate of Heaven, which is a conditional appointment rather than divinity, and that difference is the whole point of the doctrine. European monarchs were anointed and claimed divine right, and English and French kings were credited with the royal touch, curing scrofula by contact.
Frazer's Golden Bough made sacred kingship its central subject and proposed that such kings were ritually killed when their vigour declined, on the model of the priest of Nemi. The theory shaped a generation of scholarship and has not survived: the ethnographic evidence for institutional regicide is much thinner and more equivocal than Frazer supposed, and the cases he assembled have been re-examined and largely reinterpreted. The myth-and-ritual school that followed him, holding that Near Eastern kingship rituals shared a single common pattern, was similarly influential and is similarly discounted in its strong form.
What survives is a real observation without the theory attached. Rulers very frequently claim religious sanction; that claim does substantial work in securing obedience and in explaining misfortune; and traditions differ in a way that has practical consequences over whether the sanction is unconditional, as divine descent implies, or conditional on performance, as both the Mandate of Heaven and the covenantal conception of Israelite kingship imply. The second kind supplies grounds for legitimate resistance and the first does not, which is why it matters a great deal which one a tradition holds.