Caliphs are more colloquially refered to as leaders of the Muslims.The Republic of Turkey has defunct the tittle when it abolished the Ottaman Caliphate in 1924.

He/She did stuff.

The Caliph was the head of state in a Caliphate, and the title for the leader of the Islamic Ummah, an Islamic community ruled by the Shari'a.It is a transliterated version of the Arabic word خليفة KhalÄ«fah (help·info) which means "successor" or "representative". The early leaders of the Muslim nation following Muhammad's (570–632) death were called "Khalifat Rasul Allah", meaning the political successors to the messenger of God (referring to Muhammad). The question of who should succeed Muhammad was not the only issue that faced the early Muslims; they also had to clarify the extent of the leader's powers. Muhammad, during his lifetime, was not only the Muslim political leader, but the Islamic prophet. All law and spiritual practice proceeded from Muhammad. Nobody claimed that his successor would be a prophet; succession referred to political authority. The uncertainty centered on the extent of that authority. Muhammad's revelations claim to be directly from God, were soon codified and written down as the Qur'an, which was accepted as a supreme authority, limiting what a caliph could legitimately command. However, there is some evidence that some early caliphs did believe that they had authority to rule in matters not specified in the Qur'an. They believed themselves to be temporal and spiritual leaders even in issues not commanded in the Quran, and insisted that implicit obedience to the caliph in all things not contradicting the Quran, was the hallmark of the good Muslim. The modern scholars Patricia Crone and Martin Hinds, in their book God's Caliph, outline the evidence for an early, expansive view of the caliph's importance and authority. They argue that this view of the caliph was eventually nullified (in Sunni Islam, at least) by the rising power of the ulema, or Islamic lawyers, judges, scholars, and religious specialists. The ulema insisted on their right to determine what was legal and orthodox. The proper Muslim leader, in the ulema's opinion, was the leader who enforced the rulings of the ulema, rather than making rulings of his own, unless he himself was qualified in Islamic law. Conflict between caliph and ulema, akin to a modern judiciary, was a recurring theme in early Islamic history, and ended in the victory of the ulema. The caliph was henceforth limited to temporal rule only. He would be considered a righteous caliph if he were guided by the ulema. Crone and Hinds argue that Shi'a Muslims, with their expansive view of the powers of the imamate, have preserved some of the beliefs of the early Ummayad dynasty which they ironically despise. Crone and Hinds' thesis is not accepted by all scholars. Most Sunni Muslims now believe that the caliph has always been a merely temporal ruler, and that the ulema has always been responsible for adjudicating orthodoxy and Islamic law (shari'a). The first four caliphs are called the Rashidun, the Rightly Guided Caliphs, because they are believed to have followed the Qur'an and the way or sunnah of Muhammad in all things. This formulation itself presumes the Sunni ulema's view history.