Rashid al-Din Muhammad ibn Muhammad ibn Abd Jalil al-Umari, better known by his nickname of Vatvat, was a secretary, poet, philologist in the Khwarazmian Empire. In addition to being a prolific author in Arabic and Persian, he also occupied high-ranking offices, serving as the chief secretary and propagandist under the Khwarazmshahs Atsiz and Il-Arslan.

Ala al-Din wa-l-Dawla Abu'l-Muzaffar Atsiz ibn Muhammad ibn Anushtegin, better known as Atsiz (اتسز) was the second Khwarazmshah from 1127 to 1156. He was the son and successor of Muhammad I.