What was the name of Genghis Khan's eldest son?

Genghis Khan's eldest son was Jochi. He was born to Börte, Genghis Khan's first and principal wife, and became a prominent Mongol prince, military commander, and ancestor of the rulers of the Golden Horde.

Jochi's birth was surrounded by controversy because Börte had been abducted by the Merkit tribe before she was rescued. Some later accounts questioned Jochi's biological parentage, but Genghis Khan publicly recognized him as his legitimate first-born son. The issue nevertheless contributed to tension within the ruling family.

At the division of the Mongol realm in 1206, Jochi received lands and peoples in the western part of the empire. He led campaigns against the forest peoples of Siberia and helped extend Mongol authority toward the Irtysh River. His descendants later ruled the Jochid ulus, commonly known as the Golden Horde.

Jochi was not the eventual Great Khan. Genghis Khan selected Jochi's younger brother Ögedei as successor after a dispute involving Jochi and Chagatai. Jochi died in 1227, shortly before or around the time of his father's death.