Umar (Arabic: عمر ابن الخطاب, Transliteration: `Umar ibn Al-Khattāb, Umar Son of Al-Khittab, c. 586–590 CE – 7 November 644), titled Farooq the Great was the most powerful of the four Rashidun Caliphs and one of the most powerful and influential Muslim rulers in history. He was a sahabi (companion) of the prophet Muhammad (pbuh). He succeeded Caliph Abu Bakr (632–634) as the second Caliph of Rashidun Caliphate on 23 August 634. He was an expert jurist and is best known for his justice, that earned him the title Al-Farooq (The one who distinguishes between right and wrong). Under Umar the Islamic empire expanded at an unprecedented rate ruling the whole Sassanid Persian Empire and more than two-thirds of the Eastern Roman Empire. His attacks against the Sassanid Persian Empire resulted in the conquest of the Persian empire in less than two years. It was Umar, according to Jewish tradition, set aside the Christian ban on Jews and allowed Jews into Jerusalem and to worship.