An EMIR is a Muslim ruler who is usually the leader of a small state or province. A CALIPH is a Muslim ruler who is considered to be the successor of the Prophet Muhammad and is the leader of the Islamic world. A Sultan is a Muslim ruler who is the sovereign of a Muslim state. An Ameer is a Muslim ruler who is the commander of an army or a leader of a tribe. An Imam is a Muslim ruler who is the spiritual leader of a mosque or Islamic community. A Meer is a Muslim ruler who is the head of a clan or family.