Khan is a historic Turkic and Mongolic title originating among nomadic tribes in the Central and Eastern Eurasian Steppe to refer to a king. It first appears among the Rouran and then the Göktürks as a variant of khagan and implied a subordinate ruler. In the Seljuk Empire, it was the highest noble title, ranking above malik (king) and emir (prince). In the Mongol Empire it signified the ruler of a horde (ulus), while the ruler of all the Mongols was the khagan or great khan. It is a title commonly used to signify the head of a Pashtun tribe or clan.