Umar, also spelled Omar (Arabic: عمر بن الخطاب ‎, translit. ʿUmar ibn Al-Khattāb, lit. 'Umar, Son of Al-Khattab'‎, born c.583 CE – died 3 November 644 CE), was one of the most powerful and influential Muslim caliphs in history. He was a senior Sahabi of the Islamic prophet Muhammad. He succeeded Abu Bakr (632–634) as the second caliph of the Rashidun Caliphate on 23 August 634. He was an expert Islamic jurist known for his pious and just nature, which earned him the epithet Al-Farooq ("the one who distinguishes (between right and wrong)"). He is sometimes referred to as Umar I by historians of Islam, since a later Umayyad caliph, Umar II, also bore that name.

Under Umar, the caliphate expanded at an unprecedented rate, ruling the Sasanian Empire and more than two-thirds of the Byzantine Empire. His attacks against the Sasanian Empire resulted in the conquest of Persia in less than two years (642–644). According to Jewish tradition, Umar set aside the Christian ban on Jews and allowed them into Jerusalem and to worship.

Umar is revered in the Sunni tradition as a great ruler and paragon of Islamic virtues, and some hadiths identify him as the second greatest of the Sahaba after Abu Bakr. He is viewed negatively in Shia Islam.

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