Yelü Dashi
Atsiz gained his position following his father, Qutb al-Din's death in 1127. During the early part of his reign, he focused on securing Khwarazm against nomad attacks. In 1138, he rebelled against his suzerain, the Seljuq sultan Ahmad Sanjar, but was defeated in Hazarasp and forced to flee. Sanjar installed his nephew Suleiman Shah as ruler of Khwarazm and returned to Merv. Atsiz returned, however, and Suleiman Shah was unable to hold on to the province. Atsiz then attacked Bukhara, but by 1141 he again submitted to Sanjar, who pardoned him and formally returned control of Khwarazm over to him. The same year that Sanjar pardoned Atsiz, the Kara Khitai under Yelü Dashi defeated the Seljuqs at Qatwan, near Samarqand.Atsiz took advantage of the defeat to invade Khorasan, occupying Merv and Nishapur. Yelü Dashi, however, sent a force to plunder Khwarazm, forcing Atsiz to pay an annual tribute. In 1142, Atsiz was expelled from Khorasan by Sanjar, who invaded Khwarazm in the following year and forced Atsiz back into vassalage, although he continued to pay tribute to the Kara Khitai until his death. Sanjar undertook another expedition against Atsïz in 1147 when the latter became rebellious again.