The Kumo Xi (traditional Chinese: 庫莫奚; simplified Chinese: 库莫奚; pinyin: Kùmò Xī; called the Xi since the Sui dynasty (581-618 AD)), also Tatabi, were a Mongolic steppe people located in current northeast China from 207 AD to 907 AD. After the death of their ancestor Tadun in 207 they were no longer called Wuhuan but joined the Khitan Xianbei in submitting to the Yuwen Xianbei. Their history is widely linked to the more famous Khitan. During their history the Kumo Xi engaged in conflict with numerous Chinese dynasties and with the Khitans, eventually suffering a series of disastrous defeats to Chinese armies and coming under the domination of the Khitans. In 1007, the Kumo Xi were completely assimilated into the Khitan Liao Dynasty.