Umar ibn al-Khattab

'Umar was the second rightly guided caliph following Abu Bakr. A stern and convinced convert to Islam, he is sometimes compared to Christianity's St. Paul due to his history of persecuting the religion before converting to it. According to the Islamic tradition, he fought hard with Muhammad during his war against the Meccan pagans and was a man interested in military science. As caliph, he presided over the caliphate during its spectacular victories over the Byzantines and Sassanians at Yarmouk and Qadissiya, and oversaw the tremendous expansion of the caliphate into Egypt, the Levant, and Iraq. He also instituted a number of religious reforms and institutuions such as the office of the qadi. He was succeeded in his office by Uthman following his death.