Umar ibn al-Khattab 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. 586 – 644; died at about 57. Alive at the same time as Muhammad, Brahmagupta, Pseudo-Dionysius the Areopagite, Alī ibn Abī Ṭālib, and Abu Bakr. Wiki link