Mongols (And the Yuan Dynasty)
The Mongols were nomadic people, separated into small tribes, until one leader of a tribe, Genghis Khan (or Temujin), became known as the "Universal Ruler" for all of the Mongols. He was the ruler that united all the different clans and actually formed the dynasty. He led highly capable and powerful armies, which provided an immense amount of conquest.
Kublai Khan was the most influential leader of the Yuan Dynasty. He was the one that formed it, and he had gained control when they were known as the Mongols. He had a lot of power over most of China, and this led to him adopting many Chinese customs (the main reason he adopted many of the customs was to please the Chinese loyals).
The Mongols adopted siege warfare and gunpowder, which spread those two ideas around to other places. They also adopted many of the Chinese customs, furthering the spreads of certain Chinese ideas such as Buddhism, Confucianism, and Daoism, as well as many inventions.They also invented the first known postal system, the Pax Mongolica, and many new weapons and battle tactics.
The video above gives a good insight and a brief history of Ancient Korea. It mentions leaders, accomplishments, and basic facts.