 The Nizari Ismailis maintain that the Shi‘a Ismaili Imams and Ismaili Muslim thinkers have explained that al-Mahdi is not a single person but actually a function undertaken by some of the hereditary Shi‘a Ismaili Imams from the progeny of Prophet Muhammad and Imam ‘Ali ibn Abi Talib.Throughout history, only a certain number of Imams have had the practical means to undertake such a grand mission of establishing justice and equity and removing oppression and injustice from the world because most of the Ismaili Imams have been heavily persecuted.For example, the founder of the Fatimid Caliphate, Imam ‘Abdullah al-Mahdi, and the Fatimid-Imam Caliphs each performed the function or mission of the Mahdi.