THERE are a few rulers in the world who have left indelible impressions in history. Caliph Umar bin Abdul Aziz tops that list. He is considered one of the finest rulers in Muslim history, second only to the four rightly guided caliphs — Abu Bakr, Umar, Uthman and Ali (RA). In fact, in some circles, he is affectionately referred to as the fifth and the last caliph of Islam.   Umar bin Abdul Aziz ruled as a caliph for only 30 months but during this short period, he changed the world. His tenure...