My past is not a memory. It's a force at my back. It pushes and steers. I may not always like where it leads me, but like any story, the past needs resolution. What's past is prologue.

Samus Aran, the protagonist of every Metroid game. Although she is commonly a silent protagonist (excluding Metroid: Other M), a lot of her characterization and lore comes from that which is said by other characters, included in instruction manuals, or the manga (which can be read about here).

As a young girl, Samus lived a pleasant life on the mining colony of K-2L with her parents, Rodney Aran and Virginia Aran. When she was three years old, she would befriend a Chozo visitor named Old Bird. Shortly after her newfound friend left, however. . .

Her home was attacked by the species known as the Space Pirates. Lead by the dragon-like creature known as Ridley, they attacked the innocents on the colony and slaughtered everyone there, with Samus being the only survivor-- after seeing her mother killed infront of her by Ridley.

Although the Chozo would quickly return to try and lend aid, they were too late. With Samus discovered by Old Bird., they would bring her back home to their homeworld of Zebes. When there, after being informed by the Chozo's sentient AI, Mother Brain, that it was unlikely she would survive planet Zebes' harsh enviroment, she was infused with Chozo DNA to increase her chances and; when she grew older, she was given the Power Suit-- a bio-mechanical armored suit with the ability to assimilate many different weapons and function in many enviroments.

She would train for several years underneath the tutelage of her Chozo caretakers-- Old Bird and Gray Voice, before eventually enlisting in the Galactic Federation's Police Corps for several years, becoming involved with various recon missions.