The Nintendo Classic Wii Controller

Since the Nintendo Wii remote is not particularly suitable for playing Super Nintendo, Nintendo 64 or GameCube games and the Wii console is able to run games from all these systems, the Classic controller was created as a solution for playing traditional video games.

Beyond playing "classic" games, it most likely was also designed as a backup plan in case the Wii experiment failed and developers simply wanted to continue making games with traditional controls.

Like the Nunchuk attachment, the Classic controller plugs into the port on the bottom of the Wii remote. The remote may also be clipped to the bottom of the controller which would potentially also allow use of it's motion sensors while using the Classic controller.

The control layout is an evolution of both the Super Nintendo controller and the GameCube controller. (Coincidentally, the button and control layout is almost identical to my early guess at what the "Revolution" controller might have been like.)

Also see Wii remote.