The Sultan, who described himself as ‘The Second Alexander’ (Sikander-i-Sani), was Alauddin Khilji.

Alauddin Khilji was the second ruler of the Khilji dynasty in medieval India. He ascended the throne in 1296 AD after the death of his uncle and father-in-law, Jalaluddin Khilji. Alauddin Khilji is known for his military conquests and administrative reforms during his reign.

Alauddin Khilji's Ambition
Alauddin Khilji had a strong desire to expand his empire and establish his authority over a vast territory. He aimed to conquer large parts of India and emulate the achievements of Alexander the Great, the ancient Greek conqueror. To fulfill this ambition, he declared himself as 'The Second Alexander' or 'Sikander-i-Sani'.

Military Conquests
Alauddin Khilji embarked on several military campaigns to achieve his goal of territorial expansion. He successfully defeated the Mongols, who had been a constant threat to the Delhi Sultanate. He also conquered the kingdoms of Gujarat, Ranthambore, Malwa, and Chittor. His most significant military feat was the successful invasion of the Deccan region, where he defeated the Yadava dynasty and annexed their territories.

Administrative Reforms
Alauddin Khilji implemented various administrative reforms to strengthen his empire. He introduced a system of price control and market regulation to prevent hoarding and inflation. He established a network of spies to keep a check on the nobles and ensure their loyalty. He also reorganized the army and introduced a new unit called 'Chahalgani' comprising 40,000 cavalry soldiers.

Impact on the Delhi Sultanate
Alauddin Khilji's military conquests and administrative reforms had a significant impact on the Delhi Sultanate. His successful campaigns expanded the empire's boundaries and brought several regions under his direct control. His administrative reforms helped in maintaining stability and ensuring efficient governance. He also strengthened the position of the Sultanate by suppressing rebellions and centralizing power in his hands.

Conclusion
Alauddin Khilji, the second ruler of the Khilji dynasty, described himself as 'The Second Alexander' or 'Sikander-i-Sani' due to his ambitions of territorial expansion and conquest. His military conquests and administrative reforms left a lasting impact on the Delhi Sultanate, making him one of the significant rulers in medieval Indian history.