Amir al-Mu'minin

Amir al-Mu'minin (أمير المؤمنين) is usually translated Commander of the Faithful or Prince of the Faithful, but Leader of the Believers might be a better translation. It is the Arabic style of Caliphs and other independent sovereign Muslim rulers that claim legitimacy from a community of Muslims. It has been claimed as the title of rulers in Muslim countries and empires and is still used for some Muslim leaders.

Use
The title is also used by Shia Muslims to refer to their first Imam, Ali ibn Abi Talib, since he was also the Caliph. Sunni Muslims use it to refer to the first four Caliphs. It has also been adopted by various Caliphs of the succeeding Umayyad and Abbasid dynasties, as well as by some contemporary Arab monarchs.

Views of Sunni and Shi'a
Sunni view that Abu Bakr was the first person to be given the title. Shi'a view that Ali, the prophet of Islam's son-in-law and the only person to father the prophets only continuing lineage, was given the title during Muhammad's era.

Defunct offices that officially used this title

 * Various Caliphs.
 * The Taliban leader Mohammed Omar took the title while he was in control of Afghanistan.