Given the task definition and input, reply with output. In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

Who was Genghis Khan's rival?, Context: Accounts of Genghis Khan's life are marked by claims of a series of betrayals and conspiracies. These include rifts with his early allies such as Jamukha (who also wanted to be a ruler of Mongol tribes) and Wang Khan (his and his father's ally), his son Jochi, and problems with the most important shaman, who was allegedly trying to drive a wedge between him and his loyal brother Khasar. His military strategies showed a deep interest in gathering good intelligence and understanding the motivations of his rivals, exemplified by his extensive spy network and Yam route systems. He seemed to be a quick student, adopting new technologies and ideas that he encountered, such as siege warfare from the Chinese. He was also ruthless, demonstrated by his tactic of measuring against the linchpin, used against the tribes led by Jamukha.
Jamukha