Abu Ubaidah ibn al-Jarrah
In its time, the Rashidun army was a very powerful and effective force. The three most successful generals of the army were Khalid ibn al-Walid, who conquered Persian Mesopotamia and the Roman Levant, Abu Ubaidah ibn al-Jarrah, who also conquered parts of the Roman Levant, and Amr ibn al-As, who conquered Roman Egypt. The army was a key component in the Rashidun Caliphate's territorial expansion and served as a medium for the early spread of Islam into the territories it conquered.