Solid Snake (ソリッド・スネーク, Soriddo Sunēku) is a character appearing in the upcoming Super Smash Bros. Brawl. Instead of using guns like in the real games, he'll be using explosives and the cardboard box used in the trailer. He is the first third-party character to appear in any Super Smash Bros. game. Based on the most recently released trailer, Snake will have an RPG (Rocket Propelled Grenade) that he will use during gameplay. Other footage hints at a thrown grenade attack.
Snake has been seen using physical moves that look similar to those of Captain Falcon. It also looks as if Snake could be a floaty character.
Hideo Kojima, the creator of Metal Gear Solid, wished Sakurai (or "begged" according to Sakurai, himself) to include Snake in SSBM, but it was too late to do it at that time.
Sakurai has stated that he feels it would be appropriate that a "guest" character such as Snake should need to be unlocked, so it is likely that Snake will be a secret character, rather than a starter. Reasoning for this could be the fact that as of the current time, he has not been shown on Smash Bros. Dojo! at all, save the trailers. Without seeing them, a person who went to smashbros.com after May 22 would have no proof that Snake is even in the game.
As of now, none of Snake's moves have been officially unveiled, aside from possible glimpses in the second trailer.