Upon the death of the Prophet, Abu Bakr, the friend of the Prophet and the first adult male to embrace Islam, became caliph. Abu Bakr ruled for two years to be succeeded by 'Umar who was caliph for a decade and during whose rule Islam spread extensively east and west conquering the Persian empire, Syria and Egypt. It was 'Umar who marched on foot at the end of the Muslim army into Jerusalem and ordered the protection of Christian sites. 'Umar also established the first public treasury and a sophisticated financial administration. He established many of the basic practices of Islamic government.
'Umar was succeeded by 'Uthman who ruled for some twelve years during which time the Islamic expansion continued. He is also known as the caliph who had the definitive text of the Noble Quran copied and sent to the four corners of the Islamic world. He was in turn succeeded by 'Ali who is known to this day for his eloquent sermons and letters, and also for his bravery. With his death the rule of the "rightly guided" caliphs, who hold a special place of respect in the hearts of Muslims, came to an end.