Atsiz Ibn Uwaq al-Khwarizmi, also known as al-Aqsis, Atsiz ibn Uvaq, Atsiz ibn Oq and Atsiz ibn Abaq (died 1078 or 1079), was a Khwarezmian Turkish mercenary commander who established a principality in Palestine and southern Syria after seizing these from the Fatimid Caliphate in 1071. In 1076 he captured Damascus, where he began construction of the Citadel of Damascus, but an attempt to attack Cairo in the following year resulted in defeat and he was in turn forced to deal with a Fatimid advance into Syria. After appealing to the Seljuks he received assistance from Tutush, brother of the Great Seljuk sultan Malik Shah I, but was shortly afterwards imprisoned and strangled on the orders of Tutush, who proceeded to take control of his former territories.