Janamejaya was a king who lived a very long time ago in a place called India. He was very important because he was part of a very famous story called the Mahabharata.
The Mahabharata is a really long story that tells about a big war between two families. Janamejaya wasn't in the war, but he listened to the story of what happened after it was over.
One day, a man named Vyasa came to Janamejaya's palace and told him the story of the war. Vyasa had heard the story from other people, and he wrote it down so he wouldn't forget it.
Janamejaya listened to the whole story of the Mahabharata, and it took a really long time to hear it all. He learned a lot about the good and bad things people can do, and how important it is to be kind to others.
After he heard the story, Janamejaya became very famous for being a just and wise king. People admired him and looked up to him for many years. Even now, people still tell the story of Janamejaya and the Mahabharata, and they learn important lessons from it.