OTHMAN (c. 574-656)  , in full OTHMAN IBN `AFFAN, the third of the Mahommedan caliphs, a kinsman and son-in-law of Mahomet and cousin of Abu Sofii n, whose son Moawiya became the first of the Omayyad dynasty . He was elected caliph in succession to Omar in 644, but owing to his alternate weakness and cruelty and his preference of the Koreish for all responsible positions irrespective of their capacity, he produced strife throughout the empire which culminated in his assassination by Mahommed, son of Abu Bekr . He was succeeded by Ali (q.v.) . See CALIPHATE, A . § 3 .