Samus Aran is a human, born on the planet K2-L, a Federation Mining colony. When she was three years old, Space Pirates attacked the colony (as it had been previously visied by the Chozo which caught their attention), and everyone was slaughtered mercilessly, including Samus' mother and father, Virginia and Rodney Aran. The Chozo then returned to K2-L, finding Samus as the only survivor. Not knowing what to do, they took Samus to their homeworld, Zebes.

Upon arriving at Zebes, their AI system, Mother Brain, informed them that a human would be unable to survive in the harsh enviroment of Zebes. In an effort to save Samus, the Chozo intergrated their own DNA into Samus, giving her enchanced abilities. She grew up with the Chozo, undergoing serious training to become a "protector of the galaxy" as the Chozo once were, while still harboring the intense hatred against Space Pirates and the need for revenge. She then left the Chozo and became a member of the Galactic Federatoin Police, where she worked alongside with two others named Kreatz and Mauk, but suddenly dissappeared. When she returned, it was as the bounty hunter Samus Aran, which is what we know her currently as today.

In her lastest mission (chronologically), Metroid: Fusion, Samus gets infected with a mysterious organism called the X parasite, which was what the Chozo originally created the Metroids to fight. In an attempt to save her, the Galactic Federation intergrated Metroid DNA into her own, fighting off the X parasite.