Explanation:

The first Sultan who requested and obtained letters of investiture from the Khalifa was Iltutmish.
The government established by the Turks was a compromise between Islamic Political Ideas and institutions on the one hand and the existing Rajput System of Government on the other. Consequently, many elements of the Rajput Political System with or without changes became part and parcel of the Turkish administration in India. Most of the Sultans kept up the pretence of regarding the Caliph as the legal sovereign while they themselves were the Caliph's representatives.
Three Sultans sought and secured a 'Mansur' or letter of investiture from the Caliph. The first among them was Iltutmish. The other two Sultans were Muhammad-bin-Tughlaq and Firoz Tughlaq.