Master Hand

The Master Hand is a boss that appears at the end of the 1-player mode, or "Classic Mode", throughout the Super Smash Bros. series. It was not technically a Nintendo character, but was featured as the main boss because the story of Super Smash Bros. implied that someone (the player) was taking their various Nintendo toys (later trophies in Super Smash Bros. Melee and Super Smash Bros. Brawl) and imagining them fight. The Master Hand represented that player facing his hand off against the character, as many children do when playing with toys and action figures. Besides slapping and punching, the Master Hand will also shoot lasers from its finger tips and form a gun to shoot Bullet Bill-like creatures.

The Master Hand would finally be seen outside of the SSB franchise when it was featured as a boss in the GBA game, Kirby and the Amazing Mirror. In Super Smash Bros. Melee, the game introduced Crazy Hand, Master Hand's new partner who twitched a lot.

The Subspace Emissary
Super Smash Bros. Brawl features a full-fledged story mode, in which the Master hand was a part of. In it, the Master Hand was apparently giving orders to Ganondorf, as well as Bowser and Wario to turn other characters into trophies and to bring the world into Subspace. It was later revealed that he was being controlled by Tabuu, and when he was finally set free, Tabuu defeated him.