Caliph is the term or title for the Islamic leader of the
Ummah, or community of Islam. It is an Anglicized/Latinized version of the Arabic word خليفة or Khalīfah, which means "successor", that is, successor to the
Muhammad. Some Orientalists wrote the title as Khalîf. The Caliph has often been referred to as Ameer al-Mumineen (أمير المؤمنين), or "Prince of the Faithful," where "Prince" is used in the context of "commander." The title has been defunct since the abolition of the
Ottoman Sultanate in 1924.
Ayatollah (Arabic: آية الله; Persian: آیتالله) is a high title given to major
Shia clergymen. The word means 'sign of God', and those who carry the title are experts in Islamic studies such as jurisprudence, ethics, philosophy and mysticism, and usually teach in schools (hawza) of Islamic sciences. Ayatollahs can reach the position of an
Marja-e-Taqlid, which allows them to issue fatāwa (plural of "fatwa"). Also see The Grand Ayatollah.
Mullah or Mawlana are Islamic clergy who have studied the Qur'an and the Hadith and are considered experts on related religious matters in this religion. The term Mullah is a variation of the word mawla(means master or lord) and Mawlana is its derivative (means my lord) and are used mainly in Central Asia and in the Sub-Continent .
Muezzin (the word is pronounced this way Turkish, Urdu, etc.; in Arabic: مؤذن [IPA: mʊʔæðːın) is any person at the mosque who makes the adhan (call to prayer) to Friday service and the five daily prayers, or Salah. Some mosques have specific places for the adhan to be made from, such as a minaret or a designated area in the mosque.
Sahib is a denoting an Islamic leader held in high regard by one or more other Muslims. The term is used almost exclusively in the sub-continent area. The term is Arabic in origin and can be translated as lord, master, or friend.
The original Muslim kings were called caliphs, or khalifas.