Abu al-'Abbas Ahmad b. al-Mustadi al-Nasir li Din Allah was the 34th Abbasid caliph [1]. Succeeding to the caliphate after his father Abu Muhammad al-Hasan b. al-Mustanjid al-Mustadi (r. 1170 to 1180 or 565 to 575 AH), he reigned from 1180 to 1225 (575 to 625 AH) [2]. He is known as one of the strong later caliphs who attempted to revive (and succeeded to an extent) the Abbasid Caliphate’s effective power from the new emerging Islamic dynasties, before it was cut short by Mongol invasions. In order to do so, he mainly shifted his focus towards the east where the ongoing collapse of the Seljuk dynasty provided opportunities. Towards the West, he remained aloof to provide help to Saladin (d. 1193) for his fight against the Crusaders, despite repeated requests. His reign is particularly known for his reorganization of the futuwwa groups and for making them into an instrument of the state, and appointing himself (i.e. the Caliph) as the ultimate spiritual head. [3] 

Al-Nasir laid down the foundation of the al-Sarai Mosque in Baghdad. It is also known as al-Nasir li-Din Allah mosque. Furthermore, he sponsored the Mosque and Mausoleum of Suhrawardi and a mausoleum for his mother, Zumurrud Khatun. 

Notes: 

1. Hartmann, "al-Nāṣir Li-Dīn Allāh," EI3. 

2. Bosworth, The New Islamic Dynasties, 6. 

3. Hartmann, "al-Nāṣir Li-Dīn Allāh," EI3. 

Sources: 

Bosworth, Clifford Edmund. The New Islamic Dynasties: A Chronological and Genealogical Manual. Enl. and Updated ed. New York: Columbia University Press, 1996. 

Hartmann, Angelika. An-Nasir Li-Din Allah (1180-1225): Politik, Religion, Kultur in Der Späten 'Abbasidenzeit

. Reprint 2014 ed. Studien Zur Geschichte Und Kultur Des Islamischen Orients; N.F. 8. Berlin; Boston: De Gruyter, 2015. 

Hartmann, Angelika. “al-Nāṣir Li-Dīn Allāh.” Encyclopaedia of Islam, Second Edition, Edited by: P. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel, W.P. Heinrichs. Consulted online on 06 April 2020 <http://dx.doi.org.ezp-prod1.hul.harvard.edu/10.1163/1573-