Al-Mustansir Billah

Abū Tamīm Ma‘ad al-Mustanṣir bi-llāh (‎; July 5, 1029 – January 10, 1094) was the eighth Fatimid Caliph from 1036 until 1094. He was one of the longest reigning Muslim rulers.
The caliph al-Mustanṣir bi-llāh was the last Imam before a disastrous split divided the caliphate in two. One part of the caliphate was loyal to al-Mustanṣir bi-llāh’s older son, Nizār al-Muṣtafā li-Dīn Allāh, who later administered from Alamūt, in Iran. The other part of the caliphate was loyal to al-Mustanṣir bi-llāh’s younger son, Aḥmad al-Mustaʿlī bi-llāh, who later administered from Cairo.
Biography.
Al-Mustansir was born in Cairo on 16th Jumada II, 420 AH, to Ali az-Zahir and Rasad, a black slave from Nubia. At the age of only eight months he was declared the heir of his father. His name was Abu Tamim Ma‘ad, surnamed al-Mustansir bil-Lah ("The Asker Of Victory From God"). He ascended to the Fatimid Caliphate's throne on 15th Shaban, 427/June 13, 1036 at the age of . During the early years of his Caliphate, state affairs were administered by his mother. His rule lasted for 60 years, the longest of all the caliphs, either in Egypt or elsewhere in Islamic states. However, Fatimid power was confined to Egypt due to conquests of the Seljuks in the Levant and Normans in Sicily and Malta. Al-Mustansir was considered incapable and as such his court was dominated by military strongmen and his mother's favourite officials, while the treasury was exhausted by factional infighting.
He had constructed a special mihrab at one of the pillars in the Mosque of Ibn Tulun. Atop the mihrab, his name is engraved along with the Shahada commonly recited by the public in the Fatimid era ending with the phrase 'Ali-un-Wali-ul-lah', meaning "Ali is the Custodian of God".
Al-Mustansir's court.
Prominent Dais/Vizirs of his era are as follows:
Moulai Abadullah and Syedi Nuruddin were two Indians who visited Imam Al-Mustansir Billah in Egypt. They joined the Ismaili faith under Fatimid Dai Mu'ayyad fi'l-Din al-Shirazi, and went to India to propagate the faith.
The Ismaili da ‘wa.
During the reign of the Imam al-Mustanṣir, the Ismaili da ‘wa (“invitation”) was led, in the eastern regions, by ‘Abd al-Malik b. ‘Aṭṭāsh, who was based in Iṣfahān.  
Ibn al-Athīr (a Sunni historian) describes ‘Abd al-Malik (Ibn ‘Aṭṭāsh) as being interested in works of literature, and being a professional calligrapher. He continues by describing him as a clever, intelligent and quick thinker, and an ethical man.  
One of Ibn ‘Aṭṭāsh’s most notable students, Ḥasan-i Ṣabbāḥ became an important figure and was selected as the ḥujja or “proof” of al-Mustanṣir. This position/rank was right below the Imam in the Ismaili religious hierarchy. 
Architecture.
Prominent buildings constructed during the reign of Al-Mustansir are as follows:
Famine.
Between 457/1065 and 464/1072, famine degraded conditions in Egypt from bad to worse. Meanwhile, in 454/1062 and again in 459/1067, the struggle between the Turkish and Sudanese soldiery deteriorated into open warfare, ending in a victory for the Turks.
During this same period, Berber nomadic tribes from lower Egypt deliberately aggravated the distress by ravaging the countryside, destroying the embankments and canals of the Nile. The ten thousand animals that al-Mustansir's stables once held reportedly deteriorated to the point where only three thin horses were left; it is said that eventually al-Mustansir alone possessed a horse, and that when he rode out, the courtiers followed on foot, having no beast to carry them; it is also said that his escort once fainted from hunger as it accompanied him through the streets. As long as the calamity lasted, the condition of the country continued to decline. The protracted famine was followed inevitably by plague; whole districts were absolutely denuded of population and house after house lay empty.
Turkish mercenaries.
Concurrently, the Turkish mercenaries had drained the treasury; many of the works of art and valuables of all sorts in the palace were sold to satisfy their demands---often they themselves were the purchasers, at merely nominal prices, and resold the articles thus gained at a profit. Emeralds valued at 300,000 dinars were bought by one Turkish general for 500 dinars, and in one fortnight of the year 460/1068 articles to the value of 30,000,000 dinars were sold off to provide pay for the Turks. The precious library, which had been rendered available to the public and was one of the attractions for many who visited Cairo, was scattered; the books were torn up, thrown away, or used to light fires. At length, the Turks began fighting amongst themselves. Nasir al-Dawla ibn Hamdan, the general of the Turks, had invested the city, which was defended by the rival faction of the Turkish guard; after burning part of Fustat and defeating the defenders, he entered as conqueror. When he reached the palace, he found al-Mustansir lodged in rooms which had been stripped bare, waited on by only three slaves, and subsisting on two loaves which were sent him daily by the daughters of Ibn Babshand, the grammarian.
The victorious Turks dominated Cairo, held the successive viziers in subjection, treated al-Mustansir with contempt, and used their power to deplete the treasury by enhancing their pay to nearly twenty times its former figure. Nasir al-Dawla became so overbearing and tyrannical in his conduct that he provoked even his own followers, and so at length he was assassinated in 466/1074. Unfortunately, this left the city in a worse condition than ever, for it was now at the mercy of the various Turkish factions, who behaved no better than brigands. Conditions in Egypt continued to deteriorate, and unabated violence raged in the streets and countryside alike.
Descendants.
Using the genealogical information of the members of the Fatimid dynasty imprisoned by Saladin, and contemporary documents, the historian Paul E. Walker estimates that al-Mustansir had "at the minimum seventeen sons whose names we can recover". Indeed, he suggests that it was precisely the great number of offspring he sired during his long reign that created the succession crisis after his death.