No one knows the exact date of Genghis Khan's birth—the Mongols didn't keep records of such things because they didn't have a written language at the time— but most historians agree it was probably close to the year 1167. We know the details of his early life only because his son, Ogodei, later ordered a literate captive to write a biography, called The Secret History of the Mongols , to keep Genghis's memory alive for future generations.

Genghis's father, Yesugei, was the chief of a small and struggling clan of nomadic herders. He called his firstborn son Temujin, the name of a respected foe he had recently defeated in battle. Temujin's mother, Hoelun, was a member of the Tatar tribe, hereditary enemies of the Mongols. Following an age-old custom of the steppe, she became Yesugei's obedient wife after he abducted her...