For almost 13 centuries, from the death of the Prophet Muhammad in 632 to the overthrow of the last Ottoman caliph in 1924, the Islamic world was ruled by a caliph. 　　Translated from the Arabic ‘Khalifa’, the word ‘caliph’ means successor or deputy. The caliph was considered the successor to the Prophet Muhammad. 　　It is a term that has, at times, been abused. 　　In June 2014, a militant group calling itself the Islamic State in Iraq and the Levant (known as ISIL or ISIS) declared the establishment of a caliphate and proclaimed its leader, Abu Bakr al-Baghdadi, a caliph. This proclamation was rejected by the overwhelming majority of the world’s Muslims. 　　ISIL had attempted to appropriate a title imbued with religious and political significance – and in doing so had cast a dark shadow over a rich history. 　　This is the story of the caliph, a title that originated 1,400 years ago and that spanned one of the greatest empires the world has ever known.