Zero Suit Samus

Zero Suit Samus is confirmed to be a playable character in Super Smash Bros. Brawl. Zero Suit Samus is the armorless version of Samus Aran.

Zero Suit Samus is not exactly a new playable character. Under certain circumstances (currently unknown), Samus will remove her armor and become Zero Suit Samus. In the preview, she loses her armor when she charges up an enormous blast and shoots it, but it is unknown whether this is how to make her lose her suit.

Zero Suit Samus is faster but less powerful than when she has armor on. Her gun transforms into a whip, which is her main weapon.

Zero Suit Samus, as her name suggests somewhat, is taken from Metroid: Zero Mission, where a certain scene forces Samus to wear a jumpsuit rather than her normal suit.

Trivia

 * Zero Suit Samus' emblem in the Super Smash Bros. Series is the Screw Attack.