"Must\u0101\u2018l\u012B Ism\u0101\u02BF\u012Bl\u012B or Must\u0101\u2018l\u012B (Arabic: \u0645\u0633\u062A\u0639\u0644\u064A\u200E) is a sect of Ism\u0101'\u012Bl\u012B Shia Islam, so named for their acceptance of Al-Musta'li as the nineteenth Fatimid caliph and legitimate successor to his father, al-Mustansir. In contrast, the Niz\u0101riyya Muslims\u2014presently headed by the Aga Khan\u2014believe the rightful nineteenth caliph was Musta'l\u012B's elder brother, Niz\u0101r."@en .