Umar ibn Abd al-Aziz (2 November 682 (26th Safar, 63 AH) – February 720 (16th Rajab, 101 AH)) (Arabic: عمر بن عبد العزيز‎‎) was an Umayyad caliph who ruled from 717 to 720. He was also a cousin of the former caliph, being the son of Abd al-Malik's younger brother, Abd al-Aziz. He was also a matrilineal great-grandson of the second caliph Umar ibn Al-Khattab

Umar was born around 2 November 682 in Madina. His father ruled over Egypt as viceroy to the Caliph. He grew up and lived there until the death of his father, after which he was summoned to Damascus by Abd al-Malik and married to his daughter Fatima. His father-in-law would die soon after, and he would serve as governor of Medina under his cousin Al-Walid I.

Umar I had ordered that nobody should adulterate milk by mixing water into it. Once, while wandering about at night to inquire into the condition of people, he heard a woman asker her daughter to mix water into the milk before the day-break. The girl refused by reminding her mother of the order given by the Caliph. When the mother retorted by saying that the Caliph was not present and he would not know of it, the daughter replied that God is Omniscient even if Caliph was not present. Umar I was so pleased with the reply that he asked his son Asim to marry the girl, saying that he hoped that she will give birth to a man who would rule over Arabia. Umar II was the son of Asim's daughter from this marriage (Abdul Hakam, pp 17-18).

Unlike most rulers of that era, Umar formed a council with which he administered the province. His time in Medina was so notable that official grievances sent to Damascus all but ceased. In addition, many people emigrated to Medina from Iraq seeking refuge from their harsh governor, Al-Hajjaj bin Yousef. That angered Al-Hajjaj, and he pressed al-Walid to remove Umar. Much to the dismay of the people of Medina, al-Walid bowed to Hajjaj's pressure and dismissed Umar from his post. By this time, Umar had developed an impeccable reputation across the Islamic empire.

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