Genghis Khan's (as well as his son Ogedai) success is largely due to his lead general Subutai. The guy managed to swallow most of Asia, including the (until then) unconquerable Afghanistan and Russia (in the winter!).

He also destroyed the armies of both Hungary and Poland within 2 days of each other, over 500 kms apart. He was a gifted strategist apparently known for being able to coordinate multiple armies simultaneously and adapting his strategies to the opponent and terrain constantly. Certainly worthy of Hannibal, Vercingetorix et al.