A caliphate is a political-religious institution led by a successor of the Prophet Muhammad, who died in 632 AD. In its original form, says Carool Kersten, a senior lecturer at King’s College in London, the caliphate was based on a pre-Islamic Arab tribal custom of picking a tribe’s leader by consensus. Early Muslims adopted this model to pick Muhammad’s successor, who was known as “khalifa” in Arabic, or caliph. A caliph not only governs politically but also ensures governance in accordance with Islamic law. He rules over the Ummah, the Muslim community.