Umar

Umar ibn al-Khattab (; ), also spelled Omar, was the second Rashidun caliph, ruling from August 634 until his assassination in 644. He succeeded Abu Bakr () and is regarded as a senior companion and father-in-law of the Islamic prophet Muhammad.

Initially, Umar opposed Muhammad, who was his distant Qurayshite kinsman. However, upon converting to Islam in 616, he then became the first Muslim to openly pray at the Kaaba. He participated in nearly all of Muhammad’s battles and expeditions, and Muhammad conferred upon him the title ''al-Fārūq'' ("the Distinguisher") for his sound judgement. After Muhammad’s death in June 632, Umar pledged allegiance to Abu Bakr as the first caliph and served as his chief adviser. In 634, shortly before his death, Abu Bakr nominated Umar as his successor.

During Umar’s reign, the caliphate expanded at an unprecedented rate, conquering the Sasanian Empire and more than two-thirds of the Byzantine Empire. According to Jewish tradition, Umar lifted the Christian ban on Jews entering Jerusalem and permitted them to worship there. Umar was assassinated by the Persian slave Abu Lu'lu'a Firuz in 644.

Umar is widely credited with expanding the Islamic world beyond Arabia and introducing the Hijri Calendar. Historians generally regard him as one of the most powerful and influential Muslim caliphs in history. In Sunni Islamic tradition, he is revered as a just ruler and a paragon of Islamic virtues, with some hadiths identifying him as the second greatest of the Sahabah after Abu Bakr. In Twelver Shia tradition, however, he is viewed negatively. Provided by Wikipedia