The Metroid Prime franchise is a subset of the larger Metroid series set between the events of the original Metroid (and its remake Zero Mission) and Metroid II: Return of Samus. It is set apart from the rest of the Metroid series due to its first-person gameplay set in three-dimensional environments. The main trilogy of the Metroid Prime series, consisting of Metroid Prime, Metroid Prime 2: Echoes, and Metroid Prime 3: Corruption, as well as the compilation Metroid Prime Trilogy were all developed by Retro Studios along with members from Nintendo's EAD and R&D1 divisions.
To date, the Metroid Prime series has also seen two spin-offs. Metroid Prime Pinball is a DS pinball game with tables inspired by locations from the original Metroid Prime. Metroid Prime Hunters is a full first-person adventure also for the DS set between the events of Metroid Prime and Metroid Prime 2. An early demo for Hunters entitled Metroid Prime Hunters: First Hunt was bundled with the original model of Nintendo DS at the handheld's launch.
The original Metroid Prime saw Samus explore the planet Tallon IV, where she once again fought Space Pirates before encountering a new threat in the form of a material called Phazon. This substance has a highly corrupting influence on those it infects. The eponymous Metroid Prime that the original game is named for is in actuality a Metroid that had been subjected to massive amounts of Phazon. At the game's end, Samus defeats the mutated Metroid, but the Metroid would come back to life through the power of Phazon and be reborn as the creature Dark Samus, who would go on to become the main antagonist of the trilogy.