Original: The title Khan became unprecedently prominent when the tribal Mongol Temüjin proved himself a military genius by creating the Mongol empire, the greatest land empire the world ever saw, which he ruled as Genghis Khan.
Simplified: The title Khan became well known when the tribal Mongol Temüjin proved himself a military genius by creating the Mongol Empire, the greatest land empire the world ever saw, which he ruled as Genghis Khan.