The Abbasid Caliph who conferred the title of Sultan on Mahmud of Ghazni for the first time in Islamic history was Al-Qadir.

Al-Qadir's Reign:
- Al-Qadir bin Al-Muqtadir was the Abbasid Caliph who ruled from 991 to 1031 AD.
- He was known for his long and eventful reign, which witnessed both internal and external challenges.
- During his reign, the Abbasid Caliphate was in a weakened state, and the caliphs held limited political and military power.

Mahmud of Ghazni:
- Mahmud of Ghazni was the ruler of the Ghaznavid Empire, which was centered in present-day Afghanistan and parts of Iran, Pakistan, and India.
- He was a patron of arts and sciences and a great military conqueror.
- Mahmud undertook a series of military campaigns, known as the Ghaznavid invasions, to establish his dominance in the region.

Conferring the Title of Sultan:
- The title of Sultan was traditionally associated with the rulers of the Seljuk Empire, who were powerful Turkic leaders.
- Mahmud's military successes and his role in expanding the Ghaznavid Empire made him a formidable ruler.
- It is believed that in recognition of his achievements, Al-Qadir conferred on Mahmud the title of Sultan, which symbolized his authority and legitimacy as a ruler.

Significance:
- This event marked the first time in Islamic history that the title of Sultan was conferred on a ruler who was not from the Seljuk dynasty.
- It highlighted Mahmud's status as a powerful and influential ruler in the region.
- The title of Sultan became associated with rulers who held significant political and military power, and it continued to be used by subsequent Muslim rulers.

In conclusion, Al-Qadir, the Abbasid Caliph, conferred the title of Sultan on Mahmud of Ghazni, recognizing his achievements and establishing him as a powerful ruler in the Islamic world. This event marked an important development in Islamic history, as it was the first time the title of Sultan was conferred on a non-Seljuk ruler.