The first Metroid game takes place on the planet Zebes. Samus Aran travels there to infiltrate a Space Pirate base and stop experiments intended to turn Metroids into biological weapons.
Zebes is a large, hostile world dominated by underground caverns, labyrinthine rooms, elevators, and interconnected regions. In the original 1986 game, Samus explores areas such as Brinstar and Norfair before confronting major Space Pirate defenses, including Kraid, Ridley, and the biomechanical leader Mother Brain. The open-ended layout helped define Metroid's exploration-focused gameplay.
Zebes also has deep significance in Samus's backstory. After the Space Pirates attacked her home colony, the Chozo took Samus to Zebes, raised her there, and helped shape her into a warrior. The planet later became a major Chozo site and a Space Pirate stronghold. It returns as the principal setting of Super Metroid, where the Pirates rebuild their base after the events of the first game.
A common mix-up is SR388, the homeworld of the Metroid species and the setting of Metroid II: Return of Samus. Tallon IV is mainly associated with Metroid Prime, while Phaaze is a later Phazon-related world.