Why Zero Suit Samus?

Zero Suit Samus refers to Samus Aran when she is wearing her Zero Suit. The name "Zero Suit Samus" was coined in Super Smash Bros. Brawl, in which Samus appears as a playable character with and without her Power Suit.

Why does Samus wear a zero suit?

Zero Suit Samus, a playable character that Samus can turn into using her Final Smash, uses the suit to move quickly with great agility. With the Zero Suit, Samus is able to jump higher and further than a Power Suited Samus. She can rematerialize her Power Suit using her Final Smash in this form.

How did Samus get her suit?

Two specific models are well-known: the first was a suit given to Samus in her teenage years by the Chozo who raised her (seen in Metroid: Zero Mission). After being attacked by Space Pirates, Samus lost the ability to summon her suit, and was briefly forced to proceed in her Zero Suit.