The Mongols were some of the most ruthless people of that time. They learned to ride horses and use bows and arrows while on them. They razed cities to the ground and conquered all of Mongolia.
Genghis Khan, was the founder and Great Khan of the Mongolian Empire, which didn't come into full power into way after his time. He failed in attempt to rule all of China, but his family eventually achieved that.
Kublai Khan was the founder of the Yuan Dynasty. He was also a Mongolian general and statesman and was grandson of the famous Genghis Khan. Kublai Khan was the fifth great ruler of Mongolia. He eventually conquered China wholly.