What were Umar ibn al-Khattab's greatest achievements?

Umar Ibn al-Khattab (586 CE-644 CE) was the 2nd Caliph of Islam and one of the most significant companions of the Prophet (saw). According to the Prophet's companion Abdullah ibn Mas'ud: Umar's submission to Islam was a conquest, his migration was a victory, his Imamate (period of rule) was a blessing, I have seen when we were unable to pray at the Kabah until Umar submitted, when he submitted to Islam, he fought them (the pagans) until they left us alone and we prayed. (Suyuti, The History of the Khalifas Who Took the Right Way, p. 112) The TIME journalist, Michael H. Hart cited Umar Ibn al-Khattab as the 52nd most influential man to have ever lived and the historian William Muir wrote: Omar began his reign master only of Arabia. He died the Caliph of an empire embracing some of the fairest provinces under Byzantine rule, and with Persia to boot. Yet throughout this marvelous fortune he never lost the balance of a wise and sober judgment, nor exalted himself above the frugal habit of the Arab chief." (The Caliphate: Its Rise, Decline and Fall) Umar Ibn al-Khattab (ra) had many achievements and accomplishments, some are cited below: Umar (ra) supported the Messenger's call to go public in Mecca after he embraced Islam, something the Muslims had been unable to do prior to that He was one of the ten companions to be guaranteed paradise, He was the second caliph in Islam, He entrusted Shifa Abdullah, one of Prophet’s (saw) female companions, with a public role in monitoring and supervising commercial transactions in the entire marketplace of Medinah, He expanded the caliphate at an unprecedented rate, ruling the Sasanian Empire and more than two-thirds of the Byzantine Empire. His attacks against the Sasanian Empire resulted in the conquest of Persia in under two years (642–644), He established the garrison cities of al-Fustat in Egypt and Basra and Kufah in Iraq, Umar's (ra) legendary administration is quoted by scholars throughout Islamic history, as he systematised the rule of vast territories, established the Islamic calendar, organised state pensions and upheld justice and security.