Othman Ibn Affan, the third of the caliphs, killed in Medina in 655. He was one of the earliest followers of Mohammed, whom he accompanied in his flight from Mecca to Medina, and on his return became one of his secretaries. He was designated by Omar as one of the six individuals to choose his successor, and was himself selected at the close of 644, on condition that he would govern the country according to the rules of the Koran. In 645 one of his armies reduced the province of Hama-dan, and in 646 another completed the conquest of Persia, while a third took the principal cities of eastern Africa, after defeating near Tripoli Gregorius, who commanded in the name of the Greek emperor. Incursions were also made into Nubia, and in 648 the islands of Cyprus and Rhodes were plundered, these being the first maritime expeditions undertaken by the Arabs. But although fortunate in Avar, Othman's domestic administration became unpopular on account of his partiality to his family and favorites. He lost the silver signet ring used by the prophet, and considered by the Moslems the palladium of their empire, and also gave offence by occupying the pulpit when in the mosque at prayers, instead of a few steps lower down, as had been the custom of the preceding caliphs, though not of Mohammed. The discontent broke out into an open insurrection, which was quieted with some difficulty by concessions.

But Ayesha, the widow of the prophet, bribed Othman's secretary to manage that an order to the governor of Egypt, commanding him to put to death Mohammed, son of Abubekr, should fall into the latter's hands before its delivery to the governor; whereupon Mohammed marched to Medina, entered it unopposed, and invested the palace. Deserted by his soldiers, Othman, putting the Koran in his bosom, calmly awaited his fate. He died at the age of 82, or according to some of 90 or 95. He was the first caliph who had an authentic copy of the Koran made.