The Millennium Puzzle is a fictional artifact from the popular anime and manga series Yu-Gi-Oh! It is a complex, ancient puzzle that was created over 3,000 years ago. The puzzle is shaped like a pyramid and is said to hold great power, specifically the ability to unlock the spirit of the ancient Egyptian pharaoh, Yami Yugi. In the series, the main character, Yugi Mutou, solves the Millennium Puzzle, which grants him the ability to host the spirit of Yami Yugi. This connection allows them to engage in high-stakes card games known as Duel Monsters, where they face various opponents and uncover secrets about their pasts. The puzzle symbolizes the bond between Yugi and Yami Yugi, as well as the themes of friendship and courage.