Abū al-ʿAbbās Aḥmad ibn al-Hasan al-Mustaḍīʾ (), better known by his al-Nāṣir li-Dīn Allāh (; 6 August 1158 – 5 October 1225) or simply as al-Nasir, was the Abbasid caliph in Baghdad from 1180 until his death. His literally can mean The One who Gives Victory to the Religion of God. He continued the efforts of his grandfather al-Muqtafi in restoring the caliphate to its ancient dominant role and achieved a surprising amount of success as his army even conquered parts of Iran. According to the historian, Angelika Hartmann, al-Nasir was the last effective Abbasid caliph. He was able to gain full control over Mesopotamia after 200 years of nominal rule by the Abbasids since the overtake in 945 by the Shia Buyids and later the Seljuks.

In addition to his military success al-Nasir built many monuments in Baghdad that are still standing such as Bab al-Wastani gate, Abbasid Palace of Baghdad, Zumurrud Khatun Mausoleum, he also established the mosques of Al-Sarai and Hayder-Khana.

Early life Al-Nasir was the son of Caliph al-Mustadi and a Turkic umm walad called Zumurrud (Emerald).ʻIzz al-Dīn Ibn al-Athīr, Years 589-629/1193-1231: The Ayyūbids After Saladin and the Mongol Menace, transl. D.S. Richards, (Ashgate Publishing, 2008), 260. Al-Nasir was born during the last years of his great-grandfather Al-Muqtafi's reign. Ahmad was around two years old when his great-grandfather died and then his grandfather al-Mustanjid became caliph. His grandfather ruled from March 1160 to 18 December 1170 and he was successed by al-Mustadi. His father, al-Mustadi's reign was particularly notable for its extensive construction and development activities. He is reported to have rebuilt the al-Taj Palace in Baghdad, which had originally been constructed by the 10th-century Abbasid caliph (around 902–908). His reign also witnessed major construction projects involving mosques, schools, and religious endowments. His two spouses, Sayyida Banafsha and al-Nasir's mother Zumurrud, were especially active in supporting these initiatives. Banafsha, a follower of the Hanbali school of thought, ordered the construction of a bridge in Baghdad in 570 AH/1174 CE, which was subsequently named after her.

As a young prince Ahmad received good education in Baghdad along with his siblings. He also fathered some children. Ahmad had a half brother who was born to Sharaf. She was a Turkish, and was the mother of Abu Mansur Hashim ibn Hassan al-Mustadi. In 1180, Hashim tried to gather support for himself to become caliph, however he was unsuccessful and was easily overpowered by the new caliph.

Reign Al-Nasir came to power on the 28th March 1180. His reign was unusual for the rise of the futuwwaGoshgarian 2008, p. 90. groups in his reign, connected to Baghdad's long-standing ayyarun. These urban social groups had long existed in Baghdad and elsewhere, and they were often involved in urban conflicts, especially sectarian riots. Al-Nasir made them into an instrument of his government, reorganizing them along Sufi lines and ideology. A testament to its rapid rise in influence over the region, The caliph al-Nasir approved of and supported futuwwa. In 1182, al-Nasir was initiated into the ranks of the futuwwa, donning their vestments and drinking salt water in the name of its head Shaykh.Goshgarian 2008, p. 93. Over time, the Caliph would use futuwwa as a clever means of asserting caliphal power through religious hierarchy rather than regional power. He was particularly known to distribute the vestments of futuwwa to regional leaders in an assertion of his higher-rank.Goshgarian 2008, p. 94. Though the original text of the Caliph's 1207 reform measures have been lost, reproductions describe an attempt at restructuring and institutionalizing futuwwa in a manner beneficial to Caliphal authority. One 1221 mission to Anatolia, for example, sought to propagate this reform to the Islamic frontier.Goshgarian 2008, p. 99. Its contents include such measures as a strengthening of the important of the distribution of the trousers of futuwwa by the caliph and an assertion of Caliphal responsibility in protecting buildings of the futuwwa.Goshgarian 2008, p. 100.

Ultimately, the Caliph's appropriation of futuwwa led to the flowering of literature regarding the institution. Instead of taming the brotherhoods into monolithic units of caliphal control, however, the reform measures spawned an unprecedented diversity of thought regarding the organizations, and new innovations and interpretations abounded.Goshgarian 2008, p. 91. It continued for some time after the death of its founder. Al-Nasir's attempt to restructure the institution in a manner consolidating his control over Islamic society.Goshgarian 2008, p. 92.

In the early years of his caliphate, his goal was to crush the Seljuq power and replace it with his own. He incited rebellion against the Seljuq Sultan of Persia, Toghrul III. The Khwarezm Shah, Ala ad-Din Tekish, at his instigation, attacked the Seljuq forces, and defeated them in 1194; Toghrul was killed and his head exposed in the caliph's palace. Tekish, recognized now as supreme ruler of the East, bestowed on the caliph certain provinces of Persia that had been held by the Seljuqs.

During the early years of al-Nasir's long reign, famous Islamic scholar Ibn al-Jawzi, who played an instrumental role in propagating the Hanbali school of orthodox Sunni jurisprudence in his native Baghdad. Initially maintained amicable relations with the state power by way of his friendship with the caliph's Hanbali vizier, Ibn Yūnus (d. 1197). However, after the latter's dismissal and arrest – for unknown reasons – the caliph appointed as his successor the Shia Ibn al-Ḳaṣṣāb (d. ca. 1250). Although the reasons for the matter remain unclear in the historical record, al-Nasir eventually sentenced Ibn al-Jawzi to live under house arrest for five years. One of the possible reasons for this may be that Ibn al-Jawzi's relationship with the caliph had soured after the scholar had written a direct refutation of the ruler's policy in a particular matter. After five years in exile, Ibn al-Jawzi was eventually set free due to the pleading of al-Nasir's mother, whom the various chronicles describe as "a very devout woman" who pleaded with her son to free the famous scholar. Soon after his return to Baghdad, however, Ibn al-Jawzi died, being seventy-four years old.

Al-Nasir maintain good relations with Muslim scholar and Sufi Shihab al-Din 'Umar al-Suhrawardi. From an early age onwards, Suhrawardi studied Islamic jurisprudence, law, logic, theology, Quranic studies and Hadith studies.Medieval Islamic Civilization: An Encyclopedia (2006), p. 775 Suhrawardi quickly excelled in his studies and mastered, at an early age, the Shafi'i and Hanbali school of thought. Suhrawardi was eventually designated as Shaykh al-Islam by al-Nasir.

Al-Nasir's mother Zumurrud died in December 1202–January 1203, or January–February 1203, and was buried in her own mausoleum in Sheikh Maarouf Cemetery. Her mausoleum is known as Zumurrud Khatun Mausoleum.

Al-Nasir sent his vizier to Tekish with some gifts, but the vizier irritated Tekish, who attacked the caliph's troops and routed them. Thereafter hostile relations prevailed for many years. The Caliph assassinated a governor of Tekish by using an Ismaili emissary. Tekish responded by having the body of al-Nasir's vizier, who died on a campaign against him, exhumed, and the head stuck up at Khwarizm. Irritated at this and other hostile acts, the Caliph retaliated by treating with indignity the pilgrims who came from the East under Khwarizm's flag. But beyond such poor revenge, he was powerless for any open enmity.

His support for Saladin

When Saladin approached Mosul, he faced the issue of taking over a large city and justifying the action. The Zengids of Mosul appealed to caliph al-Nasir, whose vizier favored them. An-Nasir sent Badr al-Badr (a high-ranking religious figure) to mediate between the two sides. Saladin arrived at the city on 10 November 1182. Izz ad-Din would not accept his terms because he considered them disingenuous and extensive, and Saladin immediately laid siege to the heavily fortified city.

After several minor skirmishes and a stalemate in the siege that was initiated by the caliph, Saladin intended to find a way to withdraw without damage to his reputation while still keeping up some military pressure. He decided to attack Sinjar, which was held by Izz ad-Din's brother Sharaf ad-Din. It fell after a 15-day siege on 30 December. Saladin's soldiers broke their discipline, plundering the city; Saladin managed to protect the governor and his officers only by sending them to Mosul. After establishing a garrison at Sinjar, he awaited a coalition assembled by Izz ad-Din consisting of his forces, those from Aleppo, Mardin, and Armenia. Saladin and his army met the coalition at Harran in February 1183, but on hearing of his approach, the latter sent messengers to Saladin asking for peace. Each force returned to their cities and al-Fadil wrote: "They [Izz ad-Din's coalition] advanced like men, like women they vanished."

From the point of view of Saladin, in terms of territory, the war against Mosul was going well, but he still failed to achieve his objectives and his army was shrinking; Taqi ad-Din took his men back to Hama, while Nasir ad-Din Muhammad and his forces had left. This encouraged Izz ad-Din and his allies to take the offensive. The previous coalition regrouped at Harzam some 140 km from Harran. In early April, without waiting for Nasir ad-Din, Saladin and Taqi ad-Din commenced their advance against the coalition, marching eastward to Ras al-Ein unhindered. By late April, after three days of "actual fighting", according to Saladin, the Ayyubids had captured Amid. He handed the city to Nur ad-Din Muhammad together with its stores, which consisted of 80,000 candles, a tower full of arrowheads, and 1,040,000 books. In return for a diploma—granting him the city, Nur ad-Din swore allegiance to Saladin, promising to follow him in every expedition in the war against the Crusaders, and repairing the damage done to the city. The fall of Amid, in addition to territory, convinced Il-Ghazi of Mardin to enter the service of Saladin, weakening Izz ad-Din's coalition.

Saladin attempted to gain the Caliph an-Nasir's support against Izz ad-Din by sending him a letter requesting a document that would give him legal justification for taking over Mosul and its territories. Saladin aimed to persuade the caliph claiming that while he conquered Egypt and Yemen under the flag of the Abbasids, the Zengids of Mosul openly supported the Seljuks (rivals of the caliphate) and only came to the Caliph when in need. He also accused Izz ad-Din's forces of disrupting the Muslim "Holy War" against the Crusaders, stating "they are not content not to fight, but they prevent those who can". Saladin defended his own conduct claiming that he had come to Syria to fight the Crusaders, end the heresy of the Assassins, and stop the wrong-doing of the Muslims. He also promised that if Mosul was given to him, it would lead to the capture of Jerusalem, Constantinople, Georgia, and the lands of the Almohads in the Maghreb, "until the word of God is supreme and the Abbasid caliphate has wiped the world clean, turning the churches into mosques". Saladin stressed that all this would happen by the will of God, and instead of asking for financial or military support from the Caliph, he would capture and give the Caliph the territories of Tikrit, Daquq, Khuzestan, Kish Island, and Oman.

Abbasid–Ayyubid control over Hejaz

The Abbasid caliphs maintained control and hegemony over Mecca and Medina through Ayyubid sultans, since the foundation of Ayyubid rule.