He is noted for his military prowess, commanding the forces of Muhammad(saw) and those of his immediate successors of the Rashidun Caliphate; Abu Bakr and Umar ibn al-Khattab. He has the distinction of being undefeated in over a hundred battles, against the numerically superior forces of the Byzantine Roman Empire, Sassanid Persian Empire, and their allies, he is regarded as one of the greatest military commanders in history. His greatest strategic achievements were his swift conquest of the Persian Empire and conquest of Roman Syria within three years from 633 to 636, while his greatest tactical achievements were his successful double envelopment maneuver at Walaja and his decisive victories at Firaz, Ullais and Yarmouk.