ʿUmar ibn al-Khaṭṭāb (Arabic: عمر بن الخطاب, also spelled Omar, c. 586/589 – 644) was the second Rashidun caliph. He ruled from August 634 until his assassination in 644. He succeeded Abu Bakr (r. 632–634) as the second caliph of the Rashidun Caliphate on 23 August 634. Umar was a companion of the Islamic prophet Muhammad. He was also a father-in-law of Muhammad. Umar was an expert Muslim jurist. He was known for his pious and just nature. It earned him the epithet al-Farooq. This meand "the one who distinguishes (between right and wrong)".