A man of pious disposition, Nasiruddin Mahmud (rule 1246-66) was a grandson of Iltutmish. According to some experts, he was the youngest son of Iltutmish. He succeeded Alauddin Masud Shah to the throne of Slave Dynasty at the age of sixteen.
Nasiruddin Mahmud was ill-qualified to rule. A puppet in the hands of his courtiers, he was married to the daughter of Ghiyasuddin Balban, one of the leading Turkish nobles. In reciprocation to this Balban was appointed to the post of regent (naib-i-mamlakat) and was conferred with the title of Ulugh Khan (premier Khan) by the Sultan. Except for a brief period (1253-55) when some nobles opposed to Balban instigated Nasiruddin to exile him, Balban was the de facto ruler of the Delhi Sultanate during the Sultan’s reign. Nasiruddin Mahmud died in 1266. Since he had no male heirs, he designated Balban to be the Sultan.
The fourteenth century historian Isami as well as African traveller Ibn Batuta clearly mention that Nasiruddin was murdered by Balban. However, Yayiha bin Ahmad Sarhindi, author of Tarikh-i-Mubarak Shahi, does not accuse Balban of regicide and according to him, Nasiruddin Mahmud died a natural death.