However, the story has been expanded, with extra bits touching on Samus being raised on Zebes by the Chozo and Ridley's belated arrival on Zebes. Samus Aran must infiltrate their base on Zebes to destroy both the Metroids and the base's Artificial Intelligence Mother Brain. The plot is essentially the same as the original game: the Space Pirates have come into possession of a dangerous organism called a 'Metroid', which they are cloning to create an army. Metroid: Zero Mission is a remake of the original Metroid, released for the Game Boy Advance in 2004, and the sixth game released in the Metroid series.