Umar ibn al-Khattab (in Arabic, عمر بن الخطاب) (c. 581 - November, 644), sometimes referred to as Umar Farooq or just as Omar or Umar, was from the Banu Adi clan of the Quraish tribe.

He became the second caliph of Islam (634-644) and is regarded by Sunnis as one of the first four Khulfa-e-Rashidun (in Persian and Urdu, خلفأے راشدین) (or "Rightly Guided Caliphs").

The Shi'a, however, believe that he usurped authority that properly belonged to Ali ibn Abu Talib. Sunni and Shi'a hold diametrically opposite views of Umar, as can be seen in the "Sunni view" and "Shi'a view" sections at the end of this article.

Contents
1 His early life
2 His conversion to Islam
3 Umar in Medina
4 The death of Muhammad
5 Umar's Caliphate
6 Death
7 The Sunni view of Umar
8 The Shi'a view of Umar

His early life
Umar was born in Mecca. He is said to have belonged to a middle class family. He was literate, which was uncommon in those times, and he was also well known for his physical strength, being a champion wrestler.

After his conversion to Islam, he remembered with shame and regret one action he committed while he was still a "pagan": he killed his young daughter. Female infanticide was an accepted practice among the Arabs. He is quoted as saying:

"I cried when I remembered digging a hole and burying my daughter. Whilst I was putting her in, she reached up and brushed dirt from my beard." (1, 2, 3)

His conversion to Islam
When Muhammad first declared his message of Islam, Umar resolved to defend the traditional religion of the Quraish (regarded by Muslims as idolatry). Umar was most adamant in opposing Muhammad and very prominent in persecuting the Muslims.

According to an early story, Umar is said to have resolved to assassinate Muhammad. A Muslim he met on the way told him to set his own house in order first -- his sister had converted to Islam.

Umar went to her house and found her reciting verses of the Qur'an. He became infuriated and hit her. When he saw her bleeding, he was sorry for what he had done and to please her, said he would read the sura, Ta-Ha, that she had been reading. He was so struck by the sura that he accepted Islam that day.

After that, he was as determined and impetuous in defending Islam as he had been in persecuting it.

Umar in Medina
Umar was part of the first emigration (Hijra) to Yathrib (renamed Medinat al Nabi, or simply Medina shortly thereafter) in 622 C.E. He wa present at Badr, Uhud, Khaybar, and the raid on Syria, as well as many other engagements. He was one of Muhammad's close companions.

In 625, Umar's daughter Hafsa was married to Muhammad. Muhammad's household was not always peaceful; his wives quarreled over his favors and took sides against each other. Umar was much displeased when he heard this, and according to the story, scolded her thus:

"Hafsa, the (news) has reached me that you cause Allah's Messenger (may peace be upon him) trouble. You know that Allah's Messenger (may peace be upon him) does not love you, and had I not been (your father) he would have divorced you." (On hearing this) she wept bitterly. ([1])

The death of Muhammad
Muhammad died in Medina in 632 CE. Umar is said to have at threatened to kill anybody that said that Muhammad had died. He was calmed by Abu Bakr's famous statement who said, "If anyone worshipped Muhammad, then know that Muhammad is dead, but if anyone worshipped Allah, then Allah is living and does not die." He then recited the words from the Qur'an: "Muhammad is but a messenger; messengers (the like of whom) have passed away before him. If, then, he dies or is killed, will you turn back on your heel?"

Shi'a and Sunni Muslims have sharply diffrent views regarding account of the events following Muhammad's death. See Succession to Muhammad for further details.

Abu Bakr, supported by Umar, took power after Muhammad. During Abu Bakr's short reign as caliph, Umar was one of his chief advisors. Abu Bakr nominated Umar as his successor prior to his death in 634. He was confirmed in the office thereafter. Ali ibn Abu Talib, whom many believed should have been the first caliph, was again passed over.

Umar's Caliphate
During Umar's reign, the Islamic empire grew at an unprecedented rate, taking Mesopotamia and parts of Persia from the Sassanids (effectively ending that empire), and taking Egypt, Palestine, Syria, North Africa and Armenia from the Byzantines. Many of these conquests followed the watershed Battle of Yarmuk in 636 when a Muslim army of 40,000 decisively defeated a Byzantine force numbering 120,000, permanently ending Byzantine rule south of Asia Minor. (The numbers may be inexact or exaggerated.)

In 637, after a prolonged siege of Jerusalem, the Muslims took the city. Umar was given the key to the city by the Greek Orthodox patriarch, Sophronius, and invited to pray at the Church of the Holy Sepulchre. Umar chose to pray some distance from the Church, so as not to endanger its status as a Christian temple. Fifty-five years later, the Mosque of Umar was constructed on the site where he prayed. For one version of Umar's speech to the people after the surrender of Jerusalem, see [2].

Umar undertook many administrative reforms and closely oversaw public policy, establishing an advanced administration for newly conquered lands, including several new ministries and bureaucracies, as well as ordering a census of all the Muslim territories. During his reign, the garrison cities of Basra and Kufa were founded. In 638 he extended and renovated the Grand Mosque in Mecca and the Mosque of the Prophet in Medina. He also began the process of codifying Islamic law.

Umar was known for his simple 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.

Death
Umar died in 644, the victim of an assassin's dagger. Umar's killer (Abu-Lu'lu'ah) was a Persian slave who was angered with Umar; he stabbed the Caliph six times as Umar led prayers in the Masjid al Nabawi mosque in Medina.

Umar died two days later, and was buried alongside Muhammad and Abu Bakr. Uthman ibn Affan was elected as his successor.

The Sunni view of Umar
The Sunni portray him as a strong, wise, humble and competent ruler, the great second rightously guided Caliph.

The Shi'a view of Umar
The Shi'a regard Umar as a usurper, and criticize him harshly. He is said to have questioned some of Muhammad's decisions, shown cowardice in battle, and been too harsh to his daughter when he scolded her for her behavior towards Muhammad. During the matter of the disputed succession to Muhammad, he persecuted Ali and caused the death of Muhammad's daughter Fatima Zahra. Shi'a say that Umar ruled capriciously as caliph, at times giving legal rulings which contradicted the Qur'an and sunnah.

Source: http://en.wikipedia.org/wiki/Umar_ibn_al-Khattab