What was the name of the Muslim army commander who conquered Arabia, known as “The Sword of God”?

Khālid ibn al-Walīd ibn al-Mughīrah al-Makhzūmī, commonly known as simply Khalid ibn al-Walīd, was an army commander under Abu Bakr and Umar ibn Khattab. It was under his military leadership that Arabia, for the first time in history, was united under a single political entity, the Caliphate.