The House of Plantagenet was a royal dynasty that ruled England from the late 1100s to the mid-1400s. Think of them like the grown-up kings and queens who ruled over the kingdom.
It all started with a man named Henry II. He was the king of England and married a woman named Eleanor of Aquitaine, who brought a bunch of land in France into the family. They had lots of children, including Richard the Lionheart, who went on the Crusades, and John, who would later become King John, famously known for signing the Magna Carta.
After that, there was a long line of kings and queens from the House of Plantagenet, like Edward I, who built lots of castles and fought in wars, and the Black Prince, who was known for his bravery in battle.
But things got a little crazy when Henry VI became king. He wasn't very good at ruling and some other people thought they should be king instead. This led to a lot of fighting between two groups - the Lancasters who were ruled by Henry VI, and the Yorks who wanted to be in charge instead. This was called the Wars of the Roses because the two sides had different symbols - a red rose for Lancaster and a white rose for York.
In the end, a man named Henry Tudor won the war and became the king. He married a woman named Elizabeth of York, who was from the other side, and this is how the House of Tudor began. But that's a whole other story!