The Leviathan Battleship was an organism from Phaaze outfitted with technology by the Space Pirates on board the Colossus, who had fallen under the control of Dark Samus. According to the Metroid prime Trilogy art book and Space Pirate data, some time after Dark Samus had spontaneously left the Colossus, she encountered a Leviathan during her search for Phaaze. Once she infected it with her particular strain of Phazon, she had the creature open a wormhole as a shortcut to reach her destination. Afterward, she took the Leviathan back to where she had left the Colossus and ordered the Pirates to follow her through her second trip to Phaaze. It was only after reaching the planet when the crew of the Colossus began installing cybernetic weapons, crew quarters and command consoles into the Leviathan and became their leader's flagship.
Samus Aran briefly visited this organic battleship in orbit around the Pirate Homeworld, via a Warp site on the planet, to gain control of the vessel. If Samus boarded the Leviathan before having fully explored the G.F.S Valhalla, she would learn from AU 242 that Pirate command codes were needed to allow the Federation to gain access to the creature and advised her to investigate the Valhalla for any clues left behind by the Pirate raid. Once she acquired the codes, she employed them into the command consoles located in the creature's skull to gain control of the Leviathan.
Later on, this battleship was seen under the command by Fleet Admiral Castor Dane of the Galactic Federation, warping an entire fleet (including the G.F.S Olympus) to Phaaze. Its last act was to open a Wormhole, which the Federation used to escape. However, the spacecraft was too slow to escape in time, or was purposely left behind to be destroyed, just as Phaaze exploded. The Leviathan Battleship was last seen disintegrating in the blast.