Harun al-Rashid

Hārūn al-Rashīd (Arabic: and Persian:هارون الرشيد‎ ); also spelled Harun ar-Rashid; English: Aaron the Upright, Aaron the Just, or Aaron the Rightly-Guided; (763–809) was the fifth and most famous Abbasid Caliph. He was born in Rayy, near Tehran, Iran, and lived in Baghdad, Iraq and most of his reign in Ar Raqqah at the middle Euphrates.

He ruled from 786 to 809, and his time was marked by scientific, cultural and religious prosperity. Art and music also flourished significantly during his reign. He established the library Bayt al-Hikma ("House of Wisdom"). It was during his rule that Baghdad had a period of great prosperity.

Harun al-Rashid in In High Places
Harun al-Rashid was well revered in an alternate where the Great Black Deaths killed 3/4 of the population of Europe, leaving the continent open to Muslim conquest.

Harun al-Rashid was a central figure in the Arabian Nights as in the home timeline. However, in that alternate, Harun al-Rashid was the central character of the collection, and had not been replaced by the fictional King Shayar.