Omar ibn al-Khattab (died 644) was the second caliph of the Moslems and directed the spectacular Arab conquests and organized the Arab Empire.

Because Omar was one of the most adamant opponents of Mohammed's preaching in Mecca, his dramatically sudden conversion to Islam in 615 is often regarded as a turning point in the career of the Prophet. The fierce loyalty which he gave to Mohammed, both as a warrior in the battles against the Meccans and as an adviser, was reinforced by marriage when his daughter Hafsa married the Prophet.

Nevertheless, in spite of his vigorous support of the Prophet, Omar does not figure prominently in Islamic history until the death of Mohammed in 632, and even then it is as a supporter of Abu Bakr, the first caliph, whose selection Omar imposed on the divided Moslem community by the sheer force of his own personality. Although some modern historians...