Umar was the second Rashidun Caliph and reigned during 634–644. Umar's caliphate is notable for its vast conquests, aided by brilliant field commanders, he was able to incorporate present day Iraq, Iran, Azerbaijan, Armenia, Georgia, Syria, Jordan, Palestine, Lebanon, Egypt, and part of Afghanistan, Turkmenistan and south western Pakistan into the Caliphate. During his reign, the Byzantines lost more than three fourths of their territory and in Persia, the Sassanid Empire ceased to exist.[1]