'Umar ibn 'Abd al-'Aziz was a member of the Umayyad royal family and a descendant of 'Umar ibn al-Khattab. On becoming caliph in 99 AH he gave up a life of luxury.
The histories tell us that he returned to the people lands and wealth unjustly taken by his own family and the Umayyad house, abolished unjust taxes, and devoted himself to establishing justice.
He also played a great part in preserving hadith. Imam al-Bukhari records in his Sahih that 'Umar ibn 'Abd al-'Aziz wrote to Abu Bakr ibn Hazm in Madinah: look for the hadith of the Messenger of Allah ﷺ and write it down, for I fear the loss of knowledge and the passing of the scholars.
After a rule of just two and a half years he died in 101 AH. Later scholars have even called him the fifth of the Rightly Guided Caliphs.