Jamukha (Mongolian: Жамуха) was a Mongol military and political leader and the chief rival to Temüjin (later Genghis Khan) in the unification of the Mongol tribes.
Jamukha was born in the Jadaran, a sub-tribe of the Khamag Mongol confederation, and Jamukha was an anda ("childhood friend") and a blood brother to Temüjin.
According to The Secret History of the Mongols, when Börte, wife of Temüjin, was abducted by the Three Merkits; Wang Khan, Jamukha and Temüjin combined forces against the Merkits to recover her.
In 1201, the leaders of the thirteen remaining hostile tribes (among them the Merkit, Tatar, and Naimans) and the Mongol tribes not allied with Temüjin (Jadaran, Taichuud, and others) assembled a kurultai and elected Jamukha as Gur Khan, universal ruler, a title used by the rulers of the Kara-Khitan Khanate. Jamukha's assumption of this title was the final breach between Temüjin and Jamukha, leading Temüjin to form a coalition of tribes to oppose him. In the fall of that year, a great battle broke out between Jamukha's alliance and the Keraite-Khamag Mongol alliance at the Ergune valley. This decisive battle, known as the Battle of the Thirteen sides, ended with Temüjin's victory and eventual ascension as Khan of all united Mongol tribes.
Jamukha was less successful in building a coalition. Jamukha did not recruit shepherds who lacked tribal status in the Mongol tradition. This allowed Temüjin to recover from a series of military defeats inflicted by Jamukha and to emerge victorious.