Who was the famous Islamic leader known for his role in the expansion of the Islamic empire?

A. Umar ibn al-Khattab
B. Ali ibn Abi Talib
C. Khalid ibn al-Walid
D. Muawiyah ibn Abi Sufyan

Answer: Umar ibn al-Khattab


Additional Information: Umar ibn al-Khattab's caliphate marked significant territorial expansion for the Islamic empire.