Choghtu Khong Tayiji, born T�mengken (T�mengken čoγtu qong tayiǰi, 1581_1637), was a ruler of the Khalkha Mongols. He expanded into Amdo to help the Karma sect of Tibetan Buddhism but was overthrown by G��shi Khan, who supported the rival Geluk sect.

He established a base on the Tula river. Known as an intellectual he embraced the Karma sect and built monasteries and castles.

He submitted himself to Lingdan Khan, last grand khan of the Mongols. He took part in Lingdan's campaign to Tibet to help the Karma sect although Lingdan Khan died in 1634 before they joined together. But he pursued the campaign. In the same year he conquered the T�med around K�ke Nuur and moved his base there. By request from Shamar Rabjampa he sent an army under his son Arslan to central Tibet in 1635. However, Arslan attacked his ally Tsang army. He met the fifth Dalai Lama and paid homage to Gelukpa monasteries instead of destructing them. Arslan was eventually assassinated by Choghtu's order.

The Geluk sect asked for help T�r� Bayikhu (G��shi Khan), the leader of the Khoshuud tribe of the Oyirad confederation. In 1636 T�r� Bayikhu led the Khoshuud and the J��n Ghar to Tibet. In the next year a decisive war between Choghtu Khong Tayiji and T�r� Bayikhu ended in the latter's victory and Choght was killed.

Descendants of Sutai Yeldeng, Choghtu's grandson, succeeded the jasagh of a banner in Sayin Noyan Ayimagh.

He has traditionally been portrayed as evil by the Geluk sect. On the other hand, the Mongolian movie "Tsogt tayj" (1945) treated him as a national hero. It reflected the communist regime's attitude toward Tibetan Buddhism.