The House of Yi is a family that used to rule over a country called Korea a long, long time ago. Think of it like a big game of pretend, like when you and your friends pretend to be different characters. The Yis were in charge of Korea for a really long time, and they were very important and powerful. They were like the kings and queens of the country.
The Yis did lots of important things while they were in charge. They made rules and laws for the people to follow, and they helped to run the country. Some Yis were better rulers than others, though. Some were very good at their jobs, and they made Korea a better place to live, while others were not so good, and they made things worse.
Eventually, the House of Yi lost their power, and someone else took over Korea. It's like if you were playing a game of pretend, and someone else wanted to be the king or queen, so they took over. Today, the Yis still exist as a family, but they are not rulers anymore. They are just regular people like you and me.