Samus was orphaned at the age of three, when a Space Pirate raid led by Ridley left her as Earth colony K-2L's only survivor. Later adopted by the Chozo of planet Zebes, implanted with their DNA, and trained as a warrior, she ultimately grew up to be the Power Suit-wearing, laser blasting, bounty hunter that lights us up in Super Smash Bros.
The original Metroid left the player to believe that Samus was a man, unless the game was beat within a certain time frame. Passing that challenge revealed her to be a woman, which was some much welcome characterization, though it also allowed her entry into the pantheon of over-sexualized female figures.
Samus need not fear her womanhood though. Her slender figure measures up at 6 feet 3 inches tall and weighs 198 pounds, and her athleticism is far beyond that of a normal human. She'd crush you.