Umar ibn al-Khattab

Main article: Umar ibn al-Khattab

Umar was named caliph through the same deliberation process that had brought Abu Bakr into leadership. During Umar's reign Muslims conquered Mesopotamia, parts of Persia, Egypt, Palestine, Syria, North Africa and Armenia.^{[citation needed]}
The general social and moral tone of the Muslim society at that time is well-illustrated by the words of an Egyptian who was sent to spy on the Muslims during their Egyptian campaign. He reported:
"I have seen a people, every one of whom loves death more than he loves life. They cultivate humility rather than pride. None is given to material ambitions. Their mode of living is simple... Their commander is their equal. They make no distinction between superior and inferior, between master and slave. When the time of prayer approaches, none remains behind..."
Umar (in English usually called Omar) was known for his simple, austere lifestyle. Rather than adopt the pomp and display affected by the rulers of the time, he continued to live much as he had when Muslims were poor and persecuted. In 639, his fourth year as caliph and the seventeenth year 17 since the Hijra, he decreed that the years of the Islamic era should be counted from the year of the Hijraand. Umar died in 644, after he was stabbed by Abu-Lu'lu'ah in the Masjid al Nabawi mosque in Medina.
Whilst on his deathbed, he was urged to select a successor, which he refused to do. He did however put a process in place for selection of a successor. This comprised the remaining members of the ten companions promised paradise (Al-Asharatu Mubashsharun) to elect from amongst themselves a Caliph within 3 days. The result of this process following his death was Uthman ibn Affan.

source : www.wikipedia.com