The Islamic Empire was ruled by emperors known as "Caliphs." The caliphate was a form of Islamic government led by a caliph, who was considered a religious and political successor to the Prophet Muhammad. The caliphs exercised authority over the Muslim community and were pivotal in expanding and consolidating the Islamic Empire, which spanned parts of Europe, Asia, and Africa at various points in history. The most notable caliphates include the Rashidun, Umayyad, and Abbasid caliphates, each contributing significantly to the cultural, scientific, and political achievements of the Islamic Golden Age and shaping the Muslim world.