The Master Emerald (マスターエメラルド[4] Masutā Emerarudo) is an object that appears in the Sonic the Hedgehog series. It is a massive green emerald and a mystical relic of great power that acts as a counter to the Chaos Emeralds, being the only force in the universe that possesses the ability to nullify and control their energies. This makes it a very powerful and valuable gem. The Master Emerald rests on Angel Island, usually in the Altar of Emerald, where its power keeps the island afloat in the sky; without it, the island will fall down. It also served as the prison for Chaos and Tikal, until the both of them were released in recent times. Over the last three millennia, the Emerald has been guarded by the surviving members of the Knuckles Clan in order to keep the tragedies that it has been involved in from ever repeating themselves. In the present day, its current guardian is Knuckles the Echidna, the last living descendant of the Knuckles Clan. Though there has been several attempts to steal or destroy the Master Emerald over the course of recent history, Knuckles and various other heroes have always thwarted those plans and restored the Master Emerald to its resting place on Angel Island.